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ILLINOIS BIOLOGICAL 
MONOGRAPHS 


Vol. VIII October, 1923 No. 4 


EDITORIAL COMMITTEE 


STEPHEN ALFRED FORBES WILLIAM TRELEASE 


HENRY BALDWIN WARD 


PUBLISHED UNDER THE 
AUSPICES OF THE GRADUATE SCHOOL BY 
THE UNIVERSITY OF ILLINOIS 


CopyricHt, 1924 By THE UNIVERSITY OF ILLINOIS 


Distributed October 29, 1924 


THE EXTERNAL MORPHOLOGY 
AND POSTEMBRYOLOGY OF 
NOCTUID LARVAE 


WITH EIGHT PLATES 


BY Gis So alae 
LEWIS. BRADFORD RIPLEY 


Contribution from the 
Entomological Laboratories of the University of Illinois 


No. 86 


THESIS 


SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS 
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN 
ENTOMOLOGY IN THE GRADUATE SCHOOL OF 
THE. UNIVERSITY OF ILLINOIS 


eee 1921 


TABLE OF CONTENTS 


Th a Be ne BRERA o Arca cas Dion WN Stes Bed 7 
DMEM YILSS UI ORT yo OTH AE acai S cle.) Sis cata Scie Mian MOR Terh elaiahs Wane Garmin ols a) ea tialom plots 9 
mea O10 EINE. PACED. ooo 2 Scope, pag ae doy, Metis cada cemsejasiaie gd Spa sem KOE 9 
METGOSR CIELO eran eres cere cea ae tec a eee Ee a eae ee itera ae, Mae wHenghaal 2), ilaketarete aylety9 12 
Moyaplene arts) or the Head) jai) 22.5 bors Wesel iy schatenne Win > ital elai elo elle niaiserelalale 15 
“STEMEET ITE (Este rey Peete 9 One On PO Se See eae ei BN a ACA eee 19 
SEU PA IAAL EURO Ue rave Srcyoy ancy eee cs cic eh cpa stadeie poise how ase opeTS ie chars sche eysqbinias Nave eae eeeleelecs 25 
RIEEAE TOL ent sce see tes, Arn SS, 8s ohare ge PA een Sac cia ace ye NTA fe lcs) elu. cietay aca ig aS 27 
Ee ATSOOS tse eetapee trey aia tens Sores ncereetay Soran ou ae fey a vate) cloyiase iene duce ic lake oh evens istetesy Seema 26 34 
EONS 0S Rie cn i al res aA hae a eng RAC rea NP aoa EA 37 
rad DETLOLIVLOMS toric to cioin mon ciccs ioe 5 c/a en tier etercrn: STE or stord faoreldl dealt erat sel bie nalts naleiore 37 
Peeceombary sone CGumM ES foot) aa ela d aesidtnd u's oe Ga etrwpisls ale 5 rots ENGI « wc gals 43 
Pieroni bali Sutures. ucracis erece ie oie eis vernin share esisuseal wae a iangieratene aia Gls siSiaishayastalspsin: syavens) 46 
RAPA MAMI SHOR. oie g. 5) 5 de<'s wig as sraiain edhe ate Perth te ON Re eR RID ok SL aaa cet ak le 47 
PDrenALion Of WEEOWwine FIADIE |... seicecoe cis as co voc esas acieicle ne ca ele ayes 49 
RRESISLANICE CO! SUDHIETZENEE «Ses Sai aie hoi Sein cle Mele ats So aye Aalche nes clacclme neta. 52 
Epicranial Index and Subterranean Habit. 2... 02 62. . sacl ioe soe sec eee ete 56 
Postembryology of Labium,and Spinneret... . 25... cis 6k dce cee esac s sHememies s 69 
Da ADRENSAEL Shot t  h aes tel oa ex oe G ac ete aee ial sailed Wis » ase at a aya 7S 
DRM Seo ene 5 ke te ete An eR ae eR NE Bis Sete ola tye, SIM dat wte ila av 8 suet ahanre 79 
BME fee Oye a ee aida es ha Aa vial we arnerin seals nian Ca wae Aa ae sana oe ee ee aes 80 
areal Ng AA uo lane. chin nae sah ahay Seka ayer ate ne GS e ale 0'e: 4 m/s acai g ahead ah aad 82 
MASEIMUA AERIS gone 2 ie tala PAIS e omy step niengt oie oie ith w Bia wh ate atnalale ate A aye, Sis Sin eich ote 83 
Memmtonicttarr Ghee tbe. 55 Ud fai ksltcisies nies sls SUN'S ciats alee oe Hil eae wah nrg vi kydte eterale ye 87 


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249] NOCTUID LARVAE—RIPLEY 7 


INTRODUCTION 


The principal object sought in this work is to investigate the value of 
certain more or less neglected lines of evidence as a source of phylogenetic 
information. Such evidence has been applied to the Noctuidae for the 
purpose of throwing light upon our knowledge of the structural and biolog- 
ical relationships within the family. It has also been our aim to perform 
the necessary studies preliminary to the making of natural tables for the 
identification of noctuid larvae. 

There are four kinds of evidence contributing to our knowledge of the 
phylogeny of animals: comparative anatomical, recapitulative, paleonto- 
logical, and biological. Heretofore the systematic entomologist has con- 
cerned himself almost entirely with the first of these, the second remaining 
either uninvestigated or uninterpreted, the third presenting a relatively 
scant amount of material, and the last offering a virtually untouched field 
of somewhat uncertain possibility. Not only has the worker on the taxon- 
omy of insects practically confined himself to anatomical evidence, but he 
-has, until quite recently, based his classification solely on the structure of 
adult insects. Within the last decade a few excellent researches on the 
classification of immature insects, such as Fracker’s upon lepidopter- 
ous larvae, Howard, Dyar, and Knab’s upon mosquito larvae, Edna 
Mosher’s upon the taxonomy of lepidopterous pupae, and Malloch’s 
studies upon immature Diptera, have demonstrated beyond a doubt the 
value of a morphological study of immature insects as a source of phylo- 
genetic information. 

The study of the ontogeny of insects may be conveniently divided into 
_embryology and postembryology. The latter deals with development after 
hatching from the egg. It regards the larva as a free-living embryo, and 

the pupa as representing a highly specialized stage corresponding to a 
larval stadium. We may, then, speak of larval or pupal postembryology. 

Since the earlier embryonic stages of insects must recapitulate, so far 
as the law is manifested, conditions in phylogeny prior to the appearance 
of insects, the taxonomist must look to the older embryonic stages, which 
have usually not been studied, and to the postembryonic development for 
recapitulative evidence. As might be expected from their highly adaptive 
nature, pupae reveal the working of recapitulation to a less marked extent 
than do larvae. Comstock, however, based his hypothetical ancestral 
wing venation upon the pupal wing of Hepialus, and Dr. Edna Mosher 
found that certain wingless female moths have pupal wing-pads. In 


8 ILLINOIS BIOLOGICAL MONOGRAPHS [250 


general, larval postembryology may reasonably be regarded as the princi- 
pal source of recapitulative evidence to be applied within families or smaller 
groups. A study of the later embryonic stages may, on the other hand, be 
expected to throw light upon the relationships between families and orders. 

Biology, although never serving as a basis for classification, under our 
present system, quite frequently furnishes evidence of a corroborative 
nature. For example, the peculiar scattered distribution of Peripatus is 
regarded as an indication of great phylogenetic antiquity. Physiological 
life-history in relation to taxonomy has been studied but little. Since vari- 
ous types of life-history are often found within closely related groups, no 
marked correlation is generally evident; however, when the evolution of 
life-history becomes better understood, it seems quite possible that our 
sources of phylogenetic knowledge will be further supplemented by a study 
of physiological life-history. 

This consideration of the sources of our taxonomic knowledge with 
reference to their development in entomology may be summarized thus: 
the comparative morphology of the immature stages presents a relatively 
new field of well established systematic value; recapitulation offers a practic- 
ally unexplored source of information of considerable promise, and biology 
may yield valuable evidence from the taxonomic point of view. 

In a systematic treatment of an unsatisfactorily classified group all 
evidence available should be sought. It is to be expected that neglected. 
sources of information will first be called into use in those difficult groups 
where the morphology of the adults alone has not been sufficient to bring 
about a satisfactory understanding of relationships. The Noctuidae rep- 
resent such a group. With its 3500 North American species, its many ill- 
defined genera, its striking structural uniformity, and its large number of 
extremely variable species, we are not surprised to find that systematists 
have had considerable difficulty with this family. A large proportion of 
the misnamed and unnamed Lepidoptera in collections belong to the 
Noctuidae. Its general importance is probably not surpassed by that of 
any other family of insects, containing, as it does, about one-half of the 
described Lepidoptera of North America. The great economic importance 
of the Noctuidae needs only to be mentioned. 

It is hoped that the following contribution to the larval postembryology, 
larval morphology, and general biology of the Noctuidae may not only 
demonstrate the general value of these more or less neglected sources of 
phylogenetic evidence, but may also present, in a preliminary manner, 
their application to the solving of some of the many problems of the evo- 
lution of structure and habit within the family. 


251] NOCTUID LARVAE—RIPLEY 9 


LARVAL MORPHOLOGY 


Noctuid larvae, with the exception of a few genera, are characterized 
by their marked uniformity of structure. Of these the genus Acronycta 
and its allies, whose larvae resemble those of the arctiids, with their charac- 
teristic tufts of setae, has been treated by Dyar to the number of about 
fifty species. The larvae of certain other genera look like those of the 
Geometridae, lacking one or two pairs of larvapods. For the greater part, 
however, noctuid larvae are uniform with regard to most of the characters 
used by Fracker in his key to lepidopterous larvae. The position of body- 
setae, for instance, the taxonomic value of which was early pointed out by 
Dyar and which plays an important role in Fracker’s work, is very nearly 
uniform thruout the family. The same may be said of the arrangement 
of the crochets. Certain head-structures, however, first emphasized by 
Forbes, are variable within the Noctuidae. Crumb, in his key to cut- 
worms injurious to tobacco, used various types of skin-sculpture, the 
microscopic structure of the cuticle of the body. The conspicuous varia- 
tion in the number of larvapods has, of course, long been known.. With the 
exception of Dyar’s monograph of Acronycta and its allies, and Crumb’s 
artificial key for the identification of fourteen species of tobacco cut-worms, 
we have no works dealing with the classification of noctuid larvae. Fracker, 
however, gives characters for separating the family from all others but the 
Agaristidae. He divides it into four groups, all of which are listed in 
different places in his table. The.following morphological study has been 
made to determine the taxonomic value of the structural variation which 
this family exhibits in its larvae, as well as to provide the basis for a post- 
embryological study of the group. 


FIXED PARTS OF THE HEAD 


Since the structure of the head (Figs. 1-17) of noctuid larvae does not 
differ fundamentally from that typical of the entire order, the morphologi- 
cal treatment which follows applies for the most part to lepidopterous 
larvae in general. The epicranial suture assumes the form of an inverted Y 
(Fig. 2) with the stem following the dorsal portion of the meson and the 
two arms extending ventrolaterad on either side. Since the epicranial 
stem represents the median line of dorsal closure in the embryo, the arms 
being derived from the closure on either side of the so-called unpaired 
appendage, the homology of this suture with that of the larvae of all other 
orders is unquestionable. In nymphs or adults of the Orthoptera the 


10 ILLINOIS BIOLOGICAL MONOGRAPHS [252 


antacoriae divide each epicranial arm into two portions, the ventral being 
known as the fronto-genal suture. These are homologous, therefore, with 
the ventral portions of the epicranial arms of larvae. The two large 
sclerites which are separated by the epicranial stem, lie dorsad of the arms, 
comprise the greater part of the head-capsule, and make up the vertex. 
Its apparent large size in larvae is due to the absence of compound eyes. 
Since the occipital sutures are undeveloped, the caudal extent of the vertex 
is indefinite. It has been customary to refer to the fused vertex, occiput 
and postgenae as the epicranium. The vertex of lepidopterous larvae does 
not differ from larval vertices generally in bearing the ocellarae, and an- 
tennarae. The antennarae, which bear the antennae, are distinct in the 
noctuid larvae, a generalized condition found typically in the adults 
of the more primitive orders. : 

There is but one marked indication of fundamental structural special- 
ization visible externally on the vertex of lepidopterous larvae. The ad- 
frontal sutures, which have developed solely in the larvae of this order, 
run subparallel to the epicranial arms, dividing the vertex on each side into 
two portions, the mesal one being the well known adfrontal area. Hereto- 
fore, these secondary adfrontal sutures have been generally regarded as 
the epicranial arms and vice versa. Heinrich agrees with Dampf in his 
assertion that the adfrontal sclerites are a part of the front, regarding the 
sutures between the front and adfrontals as secondary infoldings. Both 
of these investigators were aware that the pretentoria invaginate at the 
bottoms of these infoldings, a point demonstrated by Berlese one year 
previous to the publication of Dampf’s paper on case-bearing larvae. The 
interpretation of these authors necessitates the supposition that the pre- 
tentorinae were originally located on the front some distance mesad of the 
epicranial arms and that they were subsequently involved by this supposed- 
ly secondary infolding, which resulted in their present position. We shall 
present evidence which appears to show conclusively that the mesal 
sutures are the epicranial arms and that the lateral ones are secondarily 
developed. 

In the first place, the pretentorinae of the larvae of other orders, so 
far as we know, are associated with the epicranial arms. They are rarely 
situated on the front removed from primary sutures. Moreover, the epi- 
cranial stem in lepidopterous larvae, unquestionably a primary structure, 
is followed internally (Fig. 1) by a deep infolding, which is continuous with 
and exactly like those of the mesal sutures which bear the pretentorinae. 
It seems highly improbable that the former suture should be primary and 
the latter secondary, when their infoldings are continuous. The fronto- 
clypeal suture, also a primary suture beyond a doubt, is expressed internally 
by a similar infolding. This suture extends between the mesal sutures and 
does not traverse the adfrontal sclerites terminating at the lateral sutures, 


253] NOCTUID LARVAE—RIPLEY 11 


as it should if the lateral sutures were the epicranial arms. ‘ Postembryo- 
logical evidence offers still stronger support to this interpretation. The 
lateral sutures are not distinct in noctuid larvae in instars earlier than the 
penultimate. So far as we have been able to ascertain the earlier instars of 
all lepidopterous larvae lack the adfrontal area, although this point appears 
to have been generally overlooked. It is not always distinctly separated 
from the vertex even in full grown larvae. The accurate morphologist, 
Berlese, shows no trace of it in his figures of the ectal and ental aspects 
of the larval head of Acherontia. These are secondary structures appearing 
relatively late in their postembryonic development. Therefore, they can- 
not be homologous with the epicranial arms, which represent the lines of 
dorsal closure on each side of the so-called unpaired appendage in the em- 
bryonic development. 

The triangular front between the epicranial arms is separated from 
the postclypeus by a more or less distinct frontoclypeal suture. This 
suture in the more primitive insects terminates near the precoilae. In 
lepidopterous larvae this suture has migrated dorsad, its ends joining the 
epicranial arms at points considerably removed from the articulations of 
the mandibles, a condition frequently found in specialized insects. Where- 
as the position of this suture probably denotes specialization, its well 
developed condition, on the other hand, is to be regarded as a general- 
ization, since it is frequently lost in both larvae and adults of various orders. 
It is sometimes not traceable externally in noctuid larvae and is rarely as 
prominent as the clypeal suture, which marks the division between the 
preclypeus and the postclypeus. This division also denotes a primitive 
condition, as is evident from a general study of insect morphology. The 
labrum of the noctuid larva always presents the bilobed shape character- 
istic of lepidopterous larvae. 

The caudal aspect of the lepidopterous larval head shows pronounced 
and varied specialization. It seems odd that this region, which perhaps 
offers points of greater morphological interest than any other part of the 
head, should have been so utterly neglected. Prominent secondary sut- 
ures extend dorsad from the mesal edge of the postcoilae, marking the 
location of deep infoldings. The position of these sutures with reference to 
the postcoilae precludes their being homologous with the occipital sutures, 
which are always situated laterad of the postcoilae and are universally 
borne by the postgenae. It is convenient to refer to the region mesad of 
these sutures as postgenae, although it should be remembered that the 
lateral extent of the true postgenae is undefined, the occipital sutures 
being undeveloped. In all but certain of the more specialized orders the 
postgenae in both larval and adult insects are widely separated by the 
cervix. In lepidopterous larvae there has been a tendency toward the 
extension mesad and an ultimate fusion of the postgenae, resulting in a 


12 ILLINOIS BIOLOGICAL MONOGRAPHS [254 


separation of the labium from the cervix. Consequently, this appendage is 
finally borne by the postgenae instead of by the cervix, which represents 
the segment to which the labium morphologically belongs. A parallel 
specialization is exhibited by the adults of certain aculeate Hymenoptera. 

In the more generalized lepidopterous larvae of the Cossidae, Pyralidi- 
dae, and Tortricidae examined, a few species of each, we find the post- 
genae quite widely separated (Figs. 3, 4, 5). Young larvae of Thyrid- 
opteryx ephemeraeformis from the first to the fourth instars (Fig. 6) also 
reveal this condition, although these sclerites meet on the meson in the full- 
grown larvae (Fig. 7), a recapitulation to be treated later in the section on 
postembryology. Secondary sclerites are sometimes formed by a chitin- 
ization of this membrane (Fig. 4). Frequently each postgena (Fig. 5) is 
divided by an oblique secondary suture. In hesperiid larvae the postgenae 
are exceptionally widely separated, the area (Fig. 8) between them being 
uniformly and heavily chitinized, resembling the gula of the Coleoptera. 
Larvae of several families have retained but a narrow strip of cervacoria 
between the postgenae. In representatives of the Sphingidae, Saturniidae, 
Lymantriidae, and Pieridae examined, they are separated only by a suture. 
The Noctuidae (Figs. 9-12) present the same condition most frequently, 
although a narrow strip of coria often persists. 

In certain of the more specialized families, notably the Saturniidae 
and Noctuidae, the cervix caudad of the postgenae has developed a vary- 
ing number of folds, some of which have become flattened one onto the 
other, chitinized, and cemented to the postgenae, where they now resemble 
sclerites. This peculiar condition appears to reach its height in the former 
family, some of whose larvae have several such folds superimposed upon 
one another and apparently fused into a thick, heavily chitinized sclerite, 
which lies flat upon the postgenae. In the Noctuidae the most cephalic 
fold only is chitinized and fastened down in this manner, where it assumes a 
bilobed form. The dorsal portion of this cervical fold is covered by the 
membranous one which follows it, exposing the brown, flat, crescent- 
shaped ends of the bilobed first fold, so that they appear as divisions of 
the postgenae, one on each side of the meson. 

In the Noctuidae part of the secondary infolding which extends around 
the dorsal portion of the margin of the foramen separates on each side a cres- 
cent-shaped secondary sclerite (Fig. 9) from the remainder of the vertex. 
The pleural portion of the neck-membrane is fastened to this sclerite. 


ENDOSKELETON 


The tentorium of lepidopterous larvae (Figs. 3, 13, 14) is very greatly 
reduced. It is unfit for the function of support generally performed by 
this structure. In correlation with this reduction a large number of large, 
heavily chitinized infoldings have developed along certain primary and 


255] NOCTUID LARVAE—RIPLEY 13 


secondary sutures, comprising the sole endoskeleton functioning as such, 
the tentorium being not only very vestigeal but to a large extent membran- 
ous and flimsy. These secondary infoldings will be referred to as para- 
demes, a term used to designate secondary infoldings in general. 

In the order Orthoptera the pretentorinae are always found at the ends 
of the fronto-clypeal suture, this being probably the most generalized 
condition. These invaginations have migrated dorsad along the fronto- 
clypeal suture for a considerable distance in the aculeate Hymenoptera. 
A similar specialization has developed in the lepidopterous larva in a 
parallel manner, the pretentorinae being located on the epicranial arms 
(Fig. 13) usually nearer to the dorsal end of the front than to the clypeus. 
It is of interest to recall that the condition of the postgenae in these larvae 
is also parallelled in important respects by that of adult Hymenoptera. 
The position of the pretentorinae is not externally marked, since they 
invaginate at the bottoms of the epicranial parademes, large infoldings, 
which extend throughout the entire length of the epicranial suture. Each 
ribbon-like pretentorium extends caudad to a metatentorium, which it 
joins near the dorsal end of each secondary postgenal suture. The pre- 
tentoria are usually chitinized for the greater portion of their length. The 
metatentorina is also located at the bottom of a deep parademe, one of 
which arises on each side of the ventral portion of the margin of the fora- 
men. These invaginations are always to be found just mesad of a large 
tendon which is supported by the parademe. The metatentoria are short 
and membranous and are located near the dorsal ends of the secondary 
postgenal sutures. The corpotentorium persists as a fine thread originat- 
ing just caudo-mesad of the point where the pretentorium and metaten- 
torium of each side join and extend across the ventral portion of the fora- 
men between the metatentoria. In the more generalized families it is 
often thicker and sometimes heavily chitinized. It assumes the appearance 
of a delicate white thread in the Noctuidae. We are thus amply justified 
in concluding that the tentorium of lepidopterous larvae is very highly 
specialized, being not only vestigial, but also unusual in position and form. 

Heavily chitinized parademes extend the entire length of the epicran- 
ial, fronto-clypeal and secondary postgenal sutures and along the dorsal 
and lateral portions of the margin of the foramen. The latter parademe 
is divided on each side by a short suture into a ventral and a dorsal occipital 
parademe. The ventral ones are the deepest of all of these infoldings, 
bearing the metatentorinae and the tendons already mentioned. They are 
the only ones not heavily chitinized. The fronto-clypeal parademe is not 
so well developed as the others. These secondary structures serve for sup- 
port and for the attachment of muscles. They have been developed in 
correlation with the specialization by reduction which is characteristic of 
the tentorium of lepidopterous larvae. 


14 ILLINOIS BIOLOGICAL MONOGRAPHS [256 


The relative length of the epicranial stem presents more conspicuous 
variation than any other character in these larvae, except, of course, the 
number of uropods. In the majority of noctuid larvae the length of this 
suture is not strikingly different from that of the front. In certain Agro- 
tinae, however, it is reduced to its adfrontal portion and in Chamyris 
cerintha, Erastrinae, it is markedly longer than the front, all gradations 
(Figs. 2, 15-17) between these extremes being found. The shortening. of 
this suture, where it occurs, has been brought about apparently by a 
splitting apart of its two sides at the caudal end, the area between these 
separated sides being taken up by the coria continuous with the cervano- 
tum. The triangular area thus formed is known as the vertical triangle, 
although morphologically it is composed of cervacoria and a part of the 
epicranial suture greatly widened. The apex of this triangle is usually 
heavily chitinized. The shortening of the epicranial stem is correlated 
with a general shortening of the cephalic aspect of the head, which has 
probably been induced by a change in the position of the head from the 
typical vertical one with the mouth-parts directed ventrad to a some- 
what horizontal one with the mandibles directed cephalo-ventrad or cep- 
halad in extreme cases. 

The shape of the clypeus (Fig. 2) presents some variation, the fronto- 
clypeal suture being either straight or curved upward in the middle more 
or less prominently. The relative widths of the preclypeus and postclypeus 
also vary to some extent. These characters appear to be of generic value. 
The width of the labrum relative to that of the clypeus and‘the depth of 
the labral cleft present characters applying to smaller groups. This 
sclerite is rarely nearly divided into two parts as in an undetermined species 
of Catocala. 

The position of the ocellarae, although presenting no striking differences 
within the family, offers some convenient characters evidently applying 
chiefly to groups of species, although constant specific differences have 
been noticed in certain genera. In the majority of cases the distance 
between ocellarae 1 and 2 is distinctly less than that between 2 and 3, the 
line 1-2 often equalling one-half of the line 2-3. Sometimes 1 and 2 are 
nearly contiguous. 

The coloration of the head is principally cuticular and, therefore, 
practically permanent in alcohol. Such markings offer much variation 
within the family, often providing easily recognizable specific characters. 
The general scheme of coloration is usually constant within a genus. In 
some species it differs markedly according to the instar. Individual varia- 
tion is sometimes considerable. The entire head capsule is uniformly col- 
ored in but relatively few species. In these it ranges from light brown to 
nearly black according to the species. Often the vertex is darker than the 
rest of the head, the preclypeus especially being lightly pigmented. This 


257] NOCTUID LARVAE—RIPLEY 15 


condition is widely distributed throughout the family. A peculiar retic- 
ulate fuscous marking is frequently found on the vertex, where it usually 
stands out prominently against the light brown background. 

In 1896 Dyar introduced the first system for designating the setae of 
the lepidopterous larval head. He numbered those of each sclerite with 
Roman numerals from dorsal to ventral margin, departing from this scheme 
slightly on the ventral portion of the vertex. More recently Dampf has 
emphasized the taxonomic importance of the head setae in the Psychidae 
and their allies. He divided the head-setae into groups on the basis of 
the tendency exhibited to vary their position in the larvae of different 
species by groups rather than individually. This interpretation led him 
to refer to them according to these groups. In his study of microlepidop- 
terous larvae Heinrich followed the system of Dampf, which he supple- 
mented by numbering the setae, pointing out the fact that these group 
migrations are due to the contracting or expanding of the parts of the 
head-capsule. Fracker and Forbes designated the setae of the head by 
the Roman numerals of Dyar. Forbes also numbered the labral setae. 

In devising a system which may be applicable to the study of the homol- 
ogies of larval setae throughout the order, and very possibly throughout 
the larvae of different orders, it seems preferable to name them after the 
sclerites on which they occur rather than according to certain groupings 
which are not well understood, except perhaps in the few families studied 
by Dampf and Heinrich. The latter author disagrees with the former as to 
the group in which a certain seta should be included. It seems likely that 
in various families in which the trend of specialization has been divergent 
this grouping relation may be altogether different. We find in the Noctui- 
dae, for example, certain setae within one of Dampf’s groups exhibiting 
wide variation in position with reference to each other. The system of 
Dyar and Forbes, with minor changes, has, therefore, been followed in 
this paper. 

These setae may be conveniently designated by the abbreviation for 
the sclerite bearing them followed by an Arabic numeral. Thus VI refers 
to the seta typically located furthest dorsad on the epicranium. The ab- 
breviations, 0, v, a, f, c, and / stand respectively for occiput, vertex, ad- 
frontal, front, clypeus and labrum. A few minute setae hitherto disre- 
garded, although of general occurrence, have been named. This same 
system of naming has been applied to the ocellarae, oc being the abbrevi- 
ation used. 


MOVABLE PARTS OF THE HEAD 


The antennae of lepidopterous larvae appear to be generally uniform 
in structure and primary setal armature. That of Cirphis unipuncta (Figs. 
19-21) may be regarded as typical for the order. The antennaria bears a 


16 ILLINOIS BIOLOGICAL MONOGRAPHS [258 


wide antacoria, which may be infolded or extended, permitting the antenna 
to be either protruded for its full length or retracted into the head so that 
only the distal portion is exposed. The first two segments are large, the 
third much smaller and the fourth very minute. These are separated by 
well developed coriae allowing free movement at the joints. The distal 
end of the second segment bears five primary setae of characteristic form, 
which may be named by combining Roman and Arabic numerals, the 
former referring to the segment, the latter to the seta. The seta III is the 
only one of these with a normal form; II 2 is extremely long and attenuate, 
being longer than the entire antenna; II 3, II 4, and II 5 are conical, II 4 
being very minute. The distal end of the small third segment bears three 
conical setae, III 2 being midway in size between III 1 and III 3. A single 
attenuate seta is carried by the minute fourth segment. 

Forbes has shown that the first three segments vary in relative size 
and that the proximal one sometimes bears secondary setae. The figures 
of Dampf and Tragardh are the only detailed ones of the antennae of 
caterpillars known to the author. The former investigator directs attention 
to the difference in the relative size of the conical setae in the Psychidae, 
where the condition is normal, and in the Talaeporiidae and the tineid 
Adela degeerella, where these setae are unusually large. Tragardh figures a 
most interesting series, representing the reduction of the antennae of 
leaf-miners. The minute size of the distal segment together with the great 
development of the third and its setae is apparently responsible for his 
failure to recognize this last segment as such, although it is distinctly 
shown in his figures. Most of the primary setae named can be identified 
even in these aberrant antennae. Packard’s figures of the larval mouth- 
parts of Eriocephala appear to show four well developed segments, a unique 
condition for the order. 

Within the Noctuidae there appears to be no variation in the antennae 
of taxonomic value, except perhaps the amount of chitinization. This 
varies from very slight to very heavy, the heavier chitinization being cor- 
related with a darker color. The habit seems to bear no relation to the 
amount of chitinization, which varies according to the genus or sometimes 
within a genus. 

The mandibles of caterpillars have been but little studied, accurate 
figures of them being scarce in literature. They are joined to the head 
immediately mesad of the antennae by a narrow mandacoria and to the 
lateral margin of the maxillae by a wide maxacoria. A large socket, the 
preartis, on the cephalo-dorsal corner serves for the articulation with the 
precoila and a large globose condyle, the postartis, on the opposite corner 
fits into the socket of the postcoila. A small caudal extensotendon and a 
large cephalic rectotendon provide attachment for the abductor and adduc- 
tor muscles respectively. The left and right mandibles are usually unlike, 


259} NOCTUID LARVAE—RIPLEY 17 


being formed so that the dentes of one fit into the emarginations of the 
other. Each mandible bears two large primary setae on its lateral aspect. 

The great majority of caterpillars present no striking variation in the 
maxillae, although a few exceptional conditions have been recorded. 
Tragardh has discussed certain modifications found in those of the leaf- 
miners. Packard’s figures of the larval mouth-parts of Eriocephala repre- 
sent three free segments of the maxillary palpus instead of the two found 
in all families other than the Micropterygidae. Differences exist in the 
relative size of the segments in various families, as shown by the figures 
of Forbes. The noctuid larval maxilla (Figs. 24-25) is typical for the 
order, presenting the highly specialized condition found in that of all 
caterpillars. 

The labium of lepidopterous larvae exhibits a degree of specialization 
unequalled even by the maxillae. The homologizing of its parts con- 
sequently presents a difficult problem. Its condition in the Noctuidae 
appears to be fairly typical for the order, although certain types of spin- 
neret frequently occur within the family which are not generally found in 
caterpillars. The labium lies between the two maxillae, its proximal two- 
thirds being joined on each side to the cardo and stipes by a labacoria, 
which has been reduced in width to a mere suture. The submentum is 
large, as it is in the larvae of other orders, and is for the most part usually 
membranous or slightly chitinized. It is broadly attached to the ventral 
margin of the postgenae for the entire width of its proximal end by a 
narrow strip of membrane. This specialized condition has been brought 
about by the extension mesad of the postgenae, so that they separate the 
labium from the cervix, which typically bears this appendage in insects. 
The narrow strip of membrane which connects the postgenae and the 
submentum is evidently a portion of the cervacoria, which has become 
separated from the rest by the unusual development of these sclerites. 
The mesal portion of the submentum is occasionally not borne by the 
postgenae, since in many species they do not extend to the meson. A 
subtriangular sclerite located in each latero-proximal corner of the labium is 
of very frequent occurrence throughout the order and is apparently always 
present in the Noctuidae. Berlese does not figure these in his drawing of the 
mouth-parts of Acherontia, evidently considering them as secondary, if 
they occur in this species. Dampf refers to them as postmentalstiicke, a 
term previously employed by Verhoeff, also regarding them as secondary, 
while Forbes, on the other hand, believed them to constitute the sub- 
mentum, although they are not represented in several of his figures of the 
labia of caterpillars. The interpretation of the latter investigator leads 
him to consider as mentum the large membranous region regarded as 
submentum by Berlese, Dampf, and the author. The corresponding 
region in the coccinellid larvae is referred to as submentum by Gage and 


18 ILLINOIS BIOLOGICAL MONOGRAPH S [260 


that of the saw-fly larva figured by Berlese and Yuasa is so labeled. The 
absence of these sclerites in many lepidopterous larvae together with the 
fact that they are generally widely separated by the membrane and never 
constitute a single piece indicates that they represent merely two strongly 
chitinized areas of the submentum. They seem to have developed in cor- 
relation with the arms of the subcardines, whose chitinized portions lie 
adjacent to these plates of the submentum. The arms extend beneath the 
chitinized areas of the submentum and serve for the attachment of muscles, 
hence the advantage of these chitinous plates in the membrane adjacent to 
them. The membranous portion of the submentum always bears a pair of 
large setae. 

The mentum is usually reduced or undifferentiated in specialized labia, 
the submentum being well developed and the stipulae always present. In 
caterpillars the mentum is not present as a distinct area, being presumably 
fused with the stipulae, which is the condition apparently found in all 
coleopterous, trichopterous, and saw-fly larvae. In those of the Lepidop- 
tera the stipulae usually consist of a proximal chitinized ring and a distal 
membranous portion, which bears the palpigers and the vestigial glossae 
on which the spinneret is located. This area is referred to by Forbes but not 
named, whereas Berlese and Dampf consider it as the mentum. Just 
proximad of the proximal end of the spinneret on the caudal aspect there is 
a pair of minute setae. 

The chitinized portion of the palpiger is typically an incomplete ring, 
its mesal and distal portions being membranous. Dampf has suggested 
that this structure may represent the basal segment of the palpus, in which 
case the palpiger must be regarded as undifferentiated. It varies much in 
width and shape throughout the order, resembling in Enocrania and Adela 
a basal segment of the palpus. In the Noctuidae it is not closely associated 
with this appendage, assuming the form of a semicircular sclerite lying in 
the membrane distad of a stipula. The mesal end of the caudal aspect of 
this semicircular sclerite is provided with two large sensoria. A reduction of 
the chitinized area mesad of the sensoria, which has frequently taken place 
throughout the order, has left them on the mesal end of the sclerite, where 
they remain surrounded partially or entirely by chitinized rings, the rem- 
nants of a more general chitinization. In the Noctuidae, where this reduc- 
tion is usually marked, the distal sensorium is rarely completely sur- 
rounded, the ring being typically broken on its mesal side. 

The two-segmented palpus has been correctly named by previous 
workers. The membrane which bears it within the semi-circular palpiger 
is generally wide, allowing free movement of this appendage. Its proximal 
segment is cylindrical, varying from stout to slender, the former shape being 
the most usual in the order and typical for the Noctuidae. It bears a 
terminal seta usually laterad of the distal segment, a minute cylinder 


261] NOCTUID LARVAE—RIPLEY 19 


situated on the membranous end of the proximal segment. A terminal 
seta is also borne by the distal segment. These two setae are apparently 
of universal occurrence in caterpillars. 


SPINNERET 


The spinneret is located on the mesal portion of the membrane on the 
caudal aspect between the palpigers. The cephalic and lateral portions of 
its proximal end are surrounded by a semi-circular sclerite of varying width 
and shape, resembling the palpiger, although much smaller. A pair of 
sensoria are borne on the caudal aspect of this structure usually at its 
mesal ends. These sensoria are much smaller than those of the palpiger. 
A fold of membrane often extends distad from this sclerite surrounding the 
proximal end of the spinning organ, the tube through which the silk is 
extruded. This fold is usually much wider on the cephalic aspect, where it 
may assume the form of a long plate reaching nearly to the end of the 
spinning organ. Occasionally it is entirely chitinized, when it is indis- 
tinguishable from the proximal sclerite. The spinning organ varies exten- 
sively, presenting a great diversity of size, form, and modification. It 
ranges from entirely membranous to largely chitinized, from very long and 
tubular to short and flat. The silk-duct opens at its distal extremity. 

Wide differences.of opinion have been expressed as to the homology of 
this peculiar organ. A number of workers, represented by Packard, regard 
it as a modified hypopharynx, whereas Berlese and Dampf believe it to be 
formed of the fused glossae and paraglossae, the latter investigator even 
venturing to homologize the proximal sclerite and fold with the paraglossa 
and the spinning organ with the fused glossae. It seems very probable to 
the author, on the other hand, that this structure has developed secon- 
darily. Those who regard it as hypopharynx appear to be misled by insuf- 
ficient data. The silk-glands of lepidopterous larvae have reasonably been 
supposed to be the homologues of the salivary glands of the adults. Lucas 
subscribes to the same homology in the Trichoptera. The salivary glands 
of adult insects, so far as known to these investigators, opened at the base 
of the hypopharynx. Therefore, they reasoned, the silk-glands of cater- 
pillars, which they regarded as the homologues of salivary glands generally, 
would presumably open on the hypopharynx, giving rise to the belief that 
this structure had been modified into a spinneret. MacGillivray has shown, 
however, that the salivary ducts of the Entopteraria open on the glossae of 
the labium, wherever these structures can be identified, and not at the 
base of the hypopharynx as in the Exopteraria, which was evidently the 
only condition known to these earlier workers. It seems questionable, 
therefore, whether these glands are homologous in the two superorders. 
However this may be, no evidence remains in support of the old view that 


20 ILLINOIS BIOLOGICAL MONOGRAPHS [262 


the spinneret has arisen from the hypopharynx, which, as will be shown 
later, is otherwise represented in lepidopterous larvae. 

The position of the spinneret is that normally occupied by the glossae 
and paraglossae. It may represent the fusion of either or both of these 
lobes, altho its mesal position indicates that it is derived only from the 
glossae. Dampf’s homologies, where he regards the paraglossae as repre- 
sented by the proximal semicircle and the alaglossa by the spinning organ 
are, therefore, open to no serious objection by those who regard the 
spinneret as a primary structure. 

Certain biological considerations lend weight to the view that the 
spinneret has developed secondarily, being without homologue in the 
typical insectean labium. Since the spinning habit appears in insects 
only in the larvae of Entopteraria, except in the Embiidae, where the 
glands open on the legs, it is evidently a secondary acquisition, which was 
not present in ancestral insect. The widespread occurrence of silk-spinning, 
however, in the larvae of Lepidoptera, Trichoptera, Hymenoptera, and 
Diptera seems to justify the conclusion that the common ancestral larva 
of these orders spun silk, although this habit has been lost in certain groups 
of each order, as Wheeler has shown it to be in certain families of ants. 
This acquisition has apparently developed furthest in the Lepidoptera, 
although it is possible that it was at one time equally extensive in the 
other orders mentioned, having been subsequently reduced. So far as 
known the spinneret is well developed only in caterpillars, the opening of 
the silkduct in silk-spinning hymenopterous, dipterous, and trichopterous 
Jarvae being without any well developed spinning organ and usually 
represented by a small aperture located near the distal end of the labium 
and surrounded by a chitinized ring. The glossae or paraglossae are 
rarely, if ever, well developed in these larvae. The condition of these 
structures leads us to suppose that they were probably vestigial in the 
ancestral larva of these orders, from which we may reasonably conclude 
that they are not well developed in caterpillars. The spinneret, therefore, 
is apparently a secondary development which evolved in correlation with 
the extensive spinning of silk: The proximal semicircular sclerite in lepi- 
dopterous larvae appears to correspond to the chitinized ring around 
the aperture in other orders and was apparently derived from the vestigial 
glossae. Although these conclusions are by no means certain, they seem 
to be the most reasonable on the basis of the evidence available. 

The variations presented by the labium and their taxonomic value in 
the Noctuidae will now be considered. This appendage offers more exten- 
sive variation in caterpillars than any other structure, both in the form 
of its sclerites and of its distal lobes, especially of the spinneret, which 
exhibits the most diverse conditions. As Forbes has shown, the sclerites 
of the submentum present considerable differences in the extent of their 


263] NOCTUID LARVAE—RIPLEY 21 


development. In the Noctuidae, however, they do not vary markedly, 
being typically as represented in Cirphis unipuncta (Fig. 24). The chi- 
tinized areas which occasionally appear in the membranous portion of the 
submentum in other families are rarely met with in the noctuids. The 
width and shape of the chitinized portion (Figs. 24, 28, 31) of the stipulae 
varies considerably according to the genus. Much generic and some 
specific variation is also presented by the chitinized portion (Figs. 26, 28, 
31, 38, 44) of the palpiger. In the noctuids this sclerite exhibits a compara~ 
tively reduced condition and never appears as the basal segment of the 
palpus as it does in some other families. The long and slender type of 
palpus occurring in a few groups has not been found in the Noctuidae, this 
appendage exhibiting the stout form most common in the order. It varies, 
however, according to the genus or to larger groups in relative width and 
length and in the proportional size of the two segments. The setae of the 
palpus present differences within the family in form, size, and position. 
The one borne on the distal end of the proximal segment is usually located 
laterad of the minute distal segment throughout the order, although in 
certain noctuid genera it has migrated around the cephalic side of the 
distal end of the first segment until it appears mesad of the terminal seg- 
ment, as in Lycophotia margaritosa (Fig. 38), a process revealed by postem- 
bryonic development. This is the only instance known to the author where 
a seta of the head or mouth-parts appears to have migrated by itself 
uninfluenced by movements of the cuticle. Forbes notes and figures an 
exceptional condition in an unnamed species of Catocala where there is 
apparently an extra small basal segment of the palpus. A similar develop- 
ment is often present in the Catocalinae due to the globular shape of the 
coria proximad of the basal segment. The situation figured by Forbes is 
evidently due to the secondary chitinization of this coria, the distal portion 
of the labium of this species exhibiting an unusual amount of chitin gener- 
ally for a noctuid larva. 

In spite of the very extensive variety of form offered by the spinneret, 
the amount of investigation which has been performed upon this interesting 
structure is surprisingly meager. Beyond Lyonet’s figures showing the 
spinneret of Cossus cossus, those by Forbes of a species of Catocala and of 
Thyridopteryx ephemeraeformis, two by Dampf showing the mouth-parts 
of case-bearing larvae, and a short series of the labia of leaf-miners by 
Tragardh, there are no detailed representations of the spinneret known to 
the author. Yet this organ probably presents a greater range of variation 
than any other structure of lepidopterous larvae. The proximal semicir- 
cular sclerite varies much in width and shape, as Forbes has shown. It is 
typically broken on the caudal aspect, although its mesal ends (Fig. 31) 
are often joined by secondary chitinization, as in Polia renigera. This 
condition may exist in some groups as a primary one, since postembry- 


22 ILLINOIS BIOLOGICAL MONOGRAPHS [264 


ological evidence indicates that the semicircular sclerite was originally a 
complete ring, its reduction having begun on the meson and proceeded 
laterad. Its shape varies much within the family affording generic and 
specific characters. The proximal fold, which assumes a great variety of 
forms within the order, also exhibits marked differences within the family, 
ranging from membranous and rounded, the more usual condition, to 
chitinized, long and pointed, when it serves as a support (Fig. 32) for the 
spinning organ, which lies caudad of its caudal surface. This is the situa- 
tion found by Dampf in the psychid genus Eumeta, which presumably led 
him to believe that this structure represents the paraglossae. 

In three European species of Hepialus examined the spinneret is 
exceptionally long, tubular, and tapering, almost filiform, extending 
several times the length of the labial palpi. According to Packard it is well 
developed in Micropteryx, but his figures of the larval heads of Eriocephala, 
drawn from a few poorly mounted specimens, fail to show any spinneret. 
Most commonly throughout the order it is tubular, slightly tapering, 
truncate, and distinctly longer that the palpi. It is often supported 
(Fig. 32) by longitudinal chitinized areas, as in Polia renigera. In certain 
groups, notably the Sphingidaé, Noctuidae, and Nepticulidae, it is short, 
flat, and stubby, frequently exhibiting a peculiar fringe (Figs. 26, 38, 39, 
45, 46) in the two former families. When of this type in the Noctuidae the 
spinneret is often emarginate on the sides so that an upper and lower lip is 
formed, the latter usually being the longer. The lower lip may be deeply 
emarginate, as in Cirphis unipuncta (Fig. 27) or bilobed, as in many Agro- 
tinae. Both lips or the upper one only may be fringed. All stages in the 
development of the fringe are represented by various species of noctuid 
larvae. It appears to have developed on the upper lip earliest in phylogeny 
(Figs. 45, 46) appearing later (Figs. 26, 39) on both surfaces. 

With the exception of the subfiliform type of Hepialus, all forms of 
spinning organ observed in other families are represented within the Noc- 
tuidae, this family probably presenting a greater range of variation in its 
spinneret than any other. In the Agrotinae it is often much shorter than 
the palpi, flat, with upper and lower lips, and frequently bilobed or fringed, 
or it may be long and pointed, as in Chloridea. It ranges from long and 
slender to fairly stout and about equal to the palpi in length in the Hadeni- 
nae, being either truncate and fringed, as in Cirphis unipuncta, or pointed, 
as in Moliana albilinea. Most commonly it is distinctly longer than the 
palpi in this subfamily and is apparently never markedly shorter, as it is 
in the Agrotinae. In the species of Cucullinae, Phytometrinae, and Hy- 
peninae examined it is much longer than the palpi and usually tapering. 
It distinctly exceeds the palpi in length in the Catocalinae, where it ranges 
from stout to slender. The spinneret of the Acronyctinae varies from 
slightly to greatly longer than the palpi, presenting an extensive variety of 


265] NOCTUID LARVAE—RIPLEY 23 


form. Larger groups of genera or even single genera may be often sepa- 
rated by characters based on the length and form of the spinneret more 
readily than by any other means. The general type of this organ is usually 
the same for large groups. Some of the most fundamental and valuable 
characters for the taxonomic treatment of noctuid larvae are provided by 
the spinneret. The failure of previous workers to appreciate the phylo- 
genetic significance of its variations has probably been due to its small size, 
which often necessitates the removal of the labium to allow careful exami- 
nation. This operation, however, is performed with the utmost readiness 
by means of a single stroke of a needle. 

The types of spinneret within the Noctuidae, unlike those of the mandi- 
bles, can be largely correlated with biological characteristics. The amount 
of silk employed as a protective covering for the pupa varies extensively 
according to the situation in which pupation takes place, the type of loca- 
tion selected being generally characteristic for the taxonomic group. 
Noctuid larvae usually pupate either within a cocoon or a subterranean 
cell. The cocoon may be fairly dense, as in many Acronyctinae and 
Phytometrinae, to very slight, as in the genus Polia of the Hadeninae. It 
never approaches those of the Saturniidae in density or in the amount of 
silk employed, being usually very slight, although often supplemented by 
foreign matter such as leaves or grass or by setae from the verrucae in 
Acronycta, where these structures are present. Those which pupate 
beneath the soil, on the other hand, usually spin but a few threads, as in 
Cirphis unipuncta, or no silk whatever, a condition exemplified by most 
species of Agrotinae which have been reared by the author. 

This reduction in the amount of silk used for a pupal covering is also 
met with in certain other families, notably in the butterflies, where only a 
button of silk is spun for the attachment of the cremaster, in the Sphingidae, 
which usually enter the soil to pupate, spinning little or no silk, and in 
certain leaf-miners, which, according to Tragardh, have lost this habit in 
correlation with their protected habitat. The accompaniment of pupation 
beneath the soil or in similarly protected situations by a marked reduction 
_in the amount of silken covering, appears to be of general if not of universal 
occurrence. It should be noted, however, that the converse is not true, 
the naked pupae of butterflies having developed other means of protection 
than subterranean pupation. 

An interesting instance of individual variation in the amount of silk 
spun is furnished by four larvae of Polia lorea. Two were taken on the 
floor of typical Illinois forest, the other two being collected on the following 
day on the prairie, about six miles from the nearest woodland. The latter 
were feeding upon sweet clover, the former upon some plant not definitely 
known, probably Geranium maculatum, but not upon any species of Tri- 
folium, since none was present in the vicinity. The two larvae of the 


24 ILLINOIS BIOLOGICAL MONOGRAPHS [266 


prairie spun fairly dense cocoons, while a mere network of threads covered 
the pupae of the individuals collected in the forest. All four pupated on the 
surface of the ground among grass on the same day under approximately 
the same external conditions. Since both sexes were represented by those 
of the prairie, the difference in the amount of silk spun was not a sexual one. 
A question of considerable interest arises as to whether this striking. 
biological variation is to be explained by the direct effect of different food 
upon the activity of the silk-glands or upon the basis of physiological 
adjustment to environment, the pupae of the prairie requiring more protec- 
tion from the sun than those of the forest. Instances of much less pro- 
nounced individual variation in this respect have been frequently noted 
with various species reared. 

Contrary to what would perhaps be the natural supposition, the sub- 
terranean mode of life frequently exhibited by noctuid larvae, exemplified 
by the cut-worms, appears to bear no definite relation to the habit of 
pupation beneath the soil. Larvae which never enter the earth during the 
feeding period often pupate in earthen cells, while some species showing 
pronounced subterranean tendencies as larvae always spin slight cocoons 
among the debris on the surface of the ground. Similarly the Sphingidae, 
which usually undergo pupation in the earth, are never subterranean as 
larvae so far as known. The habit of pupation in the soil is a fundamental 
one which remains constant throughout large groups, whereas the degree 
of development of the subterranean mode of life in larvae is variable in 
closely related species. 

Caterpillars which spin much silk are generally provided with a long, 
slender, tubular, tapering spinneret. The short depressed type is apparent- 
ly found only in those groups whose larvae spin little or no pupal covering. 
The Sphingidae and Noctuidae which pupate in earthen cells and certain 
leaf-miners which undergo this process in their mines without spinning silk 
present this reduced type of spinneret. It has not been found to occur 
where the spinning habit is well developed. The general accompaniment 
in the Noctuidae of the short flat spinning organ by the marked reduction 
or entire loss of silk-spinning is unquestionable. Some species with the long 
type of spinneret, however, pupate in the soil, as instanced by Chloridea 
armigera. This condition is to be expected in those species whose last 
instars spin silk during the feeding period. Sidemia devastatrix has been 
observed by the author to spin a cocoon in which to undergo ecdysis, a 
peculiar habit, which, so far as known, has not been recorded for any other 
caterpillar, except for certain leaf-miners studied by Tragardh. 

The peculiar fringe borne on the distal end of the spinneret has been 
found only in noctuid and sphingid larvae with subterranean pupae. 
Although the function of this strange modification has not been definitely 
determined it seems probable that it is used as a brush to distribute a 


267] NOCTUID LARVAE—RIPLEY 25 


secretion of the silk-glands over the inner surface of the earthen cell. 
Examination of the inside of these cells seems to reveal the presence of such 
asubstance. This lining serves perhaps to render the cell waterproof or to 
prevent it from crumbling. The burrows leading to the pupal cell of 
Chloridea armigera have been observed to be fortified with a similar 
secretion of unknown origin, although the spinneret of this species bears no 
fringe. Chapman observed that the thread spun by the flat short spinneret 
of the earlier instars of the leaf-miner, Limacodes testudo, assumed the form, 
not of a thread but of “a very thin ribbon,” indicating that the semifluid 
silk may issue from the spinneret in different physical states. A micro- 
scopic study of the silk of noctuid larvae, as well as an investigation of the 
comparative morphology of the silk-press promises to throw light upon 
this question. 

Both morphological and biological evidence indicates that the long 
cylindrical spinneret represents the ancestral condition for the Noctuidae. 
The development of this type to a very marked degree in Hepialus, the well 
developed spinneret in Micropteryx, and the general occurrence of the long 
spinning-organ throughout all caterpillars seem to justify this conclusion. 
As previously stated, the widespread distribution of the silk-spinning habit 
throughout trichopterous, hymenopterous, and lepidopterous larvae and its 
appearance in those of certain dipterous families indicates its development 
at an early phylogenetic period. Its absence or reduction in members of 
these orders may reasonably be regarded as a specialization. Since the loss 
or reduction of this habit in noctuid larvae, which is evidently a biological 
departure from the ancestral condition, is generally correlated with the 
short, flat spinneret, we must conclude that this type of spinning-organ is a 
specialized one derived from the tubular type in correlation with sub- 
terranean pupation. 


PREPHARYNX 


The hypopharynx of caterpillars has been largely neglected, the sole 
morphological studies of this structure having been performed by Triagardh 
on the leaf-miners, where it frequently presents a highly modified condi- 
tion, and by DeGryse, who has written a brief paper on this subject, 
embracing a number of families. The only detailed figures of the normal 
hypopharynx of lepidopterous larvae known to the author are those by 
Dampf of two species of case-bearing caterpillars, and a few by DeGryse. 
It assumes the form of a large membranous lobe lying cephalad of the 
labium and continuous with it, and extends dorsad as a rather low mound 
forming the lower floor of the prepharynx. A narrow sclerite continuous 
with the chitinized portion of the stipula extends longitudinally on each 
side of its proximal end, corresponding apparently to the lingula shown by 
Yuasa. In many noctuid larvae the hypopharynx is distinctly divided into 


26 ILLINOIS BIOLOGICAL MONOGRAPHS [268 


a ventral portion, which follows the general contour of the labium, and a 
dorsal mound-like part, which resembles the subgusta in the Orthoptera 
(Fig. 25). Very often this division is not clearly marked, as in Dampf’s 
figure of the psychid Eumeta and in the noctuid Lycophotia margaritosa. 
The question as to whether it is primary or secondary cannot be decided 
upon the basis of our meager knowledge of the condition, generally found 
within the order. It is very possible that the dorsal portion may be homo- 
logous with the subgusta of the Orthoptera, although the entire structure 
may represent the hypopharynx, in which case the division must be 
regarded as secondary. 

The hypopharynx typically bears numerous small setae, whose distri- 
bution, form, size and number vary greatly within the family, offering 
excellent generic and specific characters. They are rarely apparently 
absent, as in Rhodophora and Xylina or may, on the other hand, cover the 
entire distal portion of the hypopharynx. Frequently the pubescence does 
not begin immediately cephalad of the labial palpi, leaving a glabrous area 
in this region, as in Monima, Epizeuxis, and Platyhypena. The setae may 
be approximately equal in length, as in Lycophotia margaritosa or longer 
toward the postpharynx, as in Nephalodes, or shorter in this region than 
the setae near the labium, as in Sidemia devastatrix. In Phytometra and 
Chloridea they are longer on the sides of the hypopharynx than in the 
middle. They may be sparse, as in Platyhypena, but are more often very 
densely distributed. They vary greatly in length, sometimes attaining that 
of the palpi, as in Cirphis unipuncta (Fig. 26), but are most frequently 
much shorter, like those of Lycophotia margaritosa (Fig. 38), or stout and 
very minute as in Agrotis ypsilon (Fig. 44). In Lycophotia infecta they are 
so short that the surface of the membrane appears granular. No correla- 
tion between these various conditions and the feeding habit has been dis- 
covered. The function of these setae is probably essentially protective, 
although they may serve as sensory organs. 

The epipharynx of lepidopterous larvae is membranous and continuous 
with the labium on its ventral and lateral margins and with the post- 
pharynx at its dorsal end (Fig. 13). It bears a pair of narrow longitudinal 
sclerites, the tormae, which lie entad of the ends of the clypeo-labral suture. 
Three stout primary setae are borne on each side in the membrane near 
the ventral margin. A fourth minute seta figured by Dampf in the psychid 
genus Eumeta has not been found in the Noctuidae. No modifications of 
the epipharynx, such as those which occur in the leaf-miners, have been 
encountered in the family. Neither the form of the torma nor the position 
of the setae is subject to marked variations. 


269] NOCTUID LARVAE—RIPLEY 27 


SETAE OF TRUNK 


A number of the earlier students of lepidopterous larvae noted the 
definite arrangement of certain setae throughout large groups, which led 
them to investigate the taxonomic value of setal position. Miiller in 1886 
and Dyar in 1894 published important works on this subject, the latter 
attempting to make a table to the families of Lepidoptera based on the 
setal pattern of the larvae. The distinction between primary and secondary 
setae was recognized by Miiller, Dyar subsequently introducing the term 
subprimary, which he applied to setae of general occurrence which are 
absent from the first instar. The most extensive researches on the setae 
of the trunk have been performed recently by Fracker in 1914 and by 
Schierbeek in 1917. The former author has provided us with a most useful 
and easily workable table for the identification of caterpillars, exclusive of 
the Noctuidae, in which work the setae play an important part. The latter 
investigator pursued the subject from the morphological point of view 
rather than from the systematic one. These two workers disagree on the 
selection of a primitive type of setal position, Fracker regarding the pro- 
thorax as presenting the more generalized position, while Schierbeek gives 
good reasons for considering the abdominal segments which bear larvapods 
as the more primitive. They hold different views, moreover, as to the 
homodynamies between thoracic and abdominal setae. On at least one 
important point they agree, namely, that verrucae correspond to single 
primary setae, the former having been developed from the latter, and, in 
certain groups, having been subsequently reduced again to single setae, 
this process being a reversible one. 

Inasmuch as an investigation purposing to settle the disagreements of 
these two workers would involve a detailed study of the larvae of the whole 
order, the disputed questions of homodynamy and primitive segments 
cannot be decided from researches on the Noctuidae alone. It is conse- 
quently not a part of the plan of this work to discuss these points. The 
treatment of the setae of the trunk here presented will be confined chiefly 
to a discussion of the variation in the setal pattern of noctuid larvae, 
exclusive of those which bear verrucae, as in Acronycta. The forms with 
tufts of setae are confined within the family to this genus and to a few 
allied ones of little importance. Since they present various stages in the 
development and reduction of verrucae, these genera promise a rich field 
for the study of the evolution of setal tufts. 

Of the various systems of naming setae which have been proposed that 
of Fracker is undoubtedly the most satisfactory. As Schierbeek states, the 
older system of numbering them has resulted in so much confusion that any 
further schemes employing numerals would only increase our difficulties. 
He rejects Fracker’s Greek letter system, apparently because he disagrees 
with the homodynamies proposed by this author, and proceeds to apply 


28 ILLINOIS BIOLOGICAL MONOGRAPHS [270 


names descriptive of the location of the setae to which they refer. We fail 
to understand why a difference of opinion as to homodynamy should render 
advisable the addition of yet a new system to our already superfluous 
supply. The fact, moreover, that particular setae may be located in widely 
different positions according to the segment and to the species opens to 
objection all names of setae descriptive of position. Schierbeek would 
change the names of the setae in instances of this sort, maintaining a 
nomenclature should provide a simple means of describing larvae, rather 
than of indicating questionable homologies. Inasmuch as the general 
progress of all morphology and of taxonomy, which should always be based 
on morphology, depends largely upon the correct homologizing of struc- 
tures, we can by no means accept this view, even in cases where the homolo- 
gies indicated by the nomenclature are doubtful. The shortness of the 
names of Greek letters compared to the very long ones proposed by Schier- 
beek also favors the use of the former. Furthermore, because of the great 
utilitarian value of Fracker’s tables, this system will probably come into 
more general use than any other. For these reasons it will be used in this 
paper so far as possible. Schierbeek’s plan of naming the types of setal 
arrangement of numerals seems very commendable. No occasion arises, 
however, for using it in this work. 

Except for the marked differences in the development of verrucae 
exhibited solely within a few genera of the Acronyctinae, the setae of 
noctuid larvae offer comparatively little variation. Certain minor varia- 
tions in their number and situation, however, are of great phylogenetic 
significance because of their fundamental nature. Figures 47, 48, and 49, 
showing the setal position in Cirphis unipuncta, represent the typical con- 
dition for the family. The naming of the setae in these figures differs 
slightly from Fracker’s labeling of those of Feltia gladiaria. As clearly 
shown, both by his own figures and by those of the author, his tau on 
segments 7 and 8 should be omega. The setae on the anal larvapod are not 
named in his figure of Feltia, where their number and position is quite 
different from that in Hepialus. Consequently the letters used to designate 
these setae may not correspond to those in Fracker’s figure of Hepialus, 
which, as he states, do not necessarily indicate homodynamy with setae 
bearing the same names on other segments. The seta on the anal segment 
of Feltia which apparently corresponds to his theta on Hepialus is primary 
in the former, since it occurs in the first instar of this species. Consequently 
it should not be called theta, which is subprimary according to Fracker. 
It is referred to as kappa in this paper. 

Certain minute setae are omitted from Fracker’s figure of Feltia. 
Omega should be present on segments 1 and 9 and the minute setae labeled 
x in our figures were either generally overlooked by him or considered as 
secondary. These seem to have escaped the notice of all workers but Forbes 


271) NOCTUID LARVAE—RIPLEY 29 


and Dampf in spite of their widespread occurrence in the order. The latter 
figures them in the psychid, Eumeta, and the former in an unnamed noctuid 
and in Incurvaria, where he labels them xa, xb, xc and xd. They have been 
found by the author in nearly all noctuids examined and in the cossid 
Zeuzera pyrina, where they are extremely minute. They are undoubtedly 
primary, since they have been seen in the first instar of Cirphis untpuncta 
and of Phytometra brassicae. They most probably occur in all newly 
hatched noctuid larvae, if not in those of all caterpillars. Their extreme 
minuteness renders necessary a most careful search in order to locate them. 
The ventral two, xc and xd, occur only on the mesothorax and metathorax 
and apparently correspond to the subprimary gamma of Fracker, which, he 
states, is primary on the prothorax. These setae perhaps represent a vesti- 
geal verruca, the two together being homologous with one seta. In 
Hepialus there are three small setae in this region instead of two, as Fracker 
has shown. On the Noctuidae either one or both of the minute setae xa 
and xb are present on all segments but the prothorax and the anal one. 
Xa of the mesothorax has apparently migrated onto the caudal margin of 
the prothorax. These two setae appear to represent but one primary one 
just as a verruca corresponds to a single seta. 

The homodynamy of these four minute setae cannot be definitely 
established without involving an extensive study of the setal patterns 
of caterpillars in general, especially of the first instars. ‘Their position, 
nevertheless, suggests homodynamy between alpha of the prothorax and 
xa plus xb of the following segments and between gamma of the former 
and xc plus xd of the mesothorax and metathorax. If this be true, beta and 
delta of the prothorax correspond respectively to alpha and beta of the 
following segments, other homodynamies remaining unchanged. This 
interpretation reveals a much closer similarity between the prothorax and 
other segments than that of Fracker, in which the minute setae were dis- 
regarded. It seems preferable, however, to retain the names of Forbes for 
these setae pending more extensive study on this question. 

Variations in the setal pattern of the prothorax are clearly discernible 
and generally fairly constant for genera but they are so slight and grade so 
continuously that very little taxonomic aid is afforded by them. The 
location of beta varies longitudinally to some extent, ranging from a 
position on the transverse line of beta to one distinctly caudad of it. Rho 
exhibits some transverse variation, being either equidistant from delta and 
the spiracle, as in Polia meditata, or much nearer to the latter, as in Nephe- 
lodes emmedonia. The situation of epsilon with reference to gamma and 
to the spiracle offers the best character in setal position on the prothorax. 
In the Acronyctinae, Cucullinae, and Hadeninae epsilon may be distinctly 
nearer to either according to the genus. It is apparently always nearer to 
the spiracle on the Catocalinae and Phytometrinae, but ranges in the 


30 ILLINOIS BIOLOGICAL MONOGRAPHS [272 


Agrotinae from a point equidistant to one much nearer to gamma. Epsilon 
also varies in position in the Hypeninae, being equidistant from gamma 
and the spiracle in some genera and nearer to the spiracle in others. Some 
longitudinal variation is offered by epsilon, which may be slightly or con- 
siderably caudad of kappa according to the genus. Kappa varies slightly 
but quite constantly in transverse location, ranging from a point distinctly 
above the spiracle to one a little below it. The relative situation of eta, 
kappa and the spiracle with reference to one another differs according to 
the group. Eta is usually distinctly below kappa and slightly caudad of it, 
being much nearer to kappa than to the spiracle. These setae may, how- 
ever, be on the same longitudinal line, with kappa so far caudad that it is 
equidistant from eta and the spiracle. 

As in caterpillars generally the mesothorax and metathorax are very 
similar to each other, although they exhibit a quite different setal pattern 
than the prothorax, the arrangement on the former segments resembling 
rather closely that of the abdominal ones. The mesothorax and metathorax 
differ from those which follow chiefly in the longitudinal position of alpha 
and beta and in the situation of the setae occupying the region which bears 
the spiracle in other segments. One or both of the minute setae xa and xb 
may be present on the mesothorax, this point representing individual varia- 
tion. Both are usually present on the metathorax. On the mesothorax 
beta varies from a position on the transverse line through alpha to one 
distinctly cephalad of it. The location of beta may be the same on the 
metathorax as on the mesothorax or it may, as is often the case, be a little 
further caudad on the metathorax (Fig. 48), the amount of variation in this 
respect remaining the same for both segments. On both mesothorax and 
metathorax rho varies longitudinally from a point distinctly cephalad 
to one a little caudad of epsilon, the latter condition being commonly found 
in the Agrotinae. A greater difference in position is presented by beta, 
which on the mesothorax may be either equidistant from alpha and epsilon 
or very much nearer to alpha as in Catocala. On the metathorax beta 
is usually further ventrad, varying the same amount as on the mesothorax. 
The position of a line drawn through rho and epsilon with reference to 
kappa and theta furnishes one of the best characters on these two segments. 
The condition in this respect is usually the same on these segments, but 
may be distinctly different as in Achatodes zeae, showing that there 
has been some independent variation in the setal position, notwith- 
standing their very similar organization. In the Agrotinae and 
Catocalinae examined this line passes nearer to theta than to kappa. 
It may be distinctly nearer to either one in the Hadeninae, Acronyctinae 
and Hypeninae according to the genus. In the Phytometrinae it is 
usually equidistant from the two setae and ranges from a point equi- 
distant to one much nearer to theta in the Cucullinae. The situation of 


273] NOCTUID LARVAE—RIPLEY 31 


kappa, theta, and eta relative to one another also varies sufficiently to 
provide some characters. Kappa may be equidistant from eta and theta 
or very much nearer to eta. Most commonly it is slightly but distinctly 
nearer to the latter, being especially close to theta in the Catocalinae, 
Phytometrinae, and Hypeninae, a group of subfamilies which, as will be 
shown later, conform as a unit to certain other very fundamental char- 
acters. The angle made at kappa by the lines kappa-eta and kappa-theta 
varies in size from 80 degrees to a very obtuse one according to the genus. 
The most marked variation in setal position exhibited on the mesothorax 
and metathorax is furnished by xc and xd. Although closely associated, 
they vary not only relative to each other but also in transverse position 
with reference to epsilon and rho, ranging from a point a little above rho to 
one slightly below epsilon, the latter condition having been found only in 
Achatodes zeae. Their minute size, however, would render impractical their 
use in tables. The fact that much greater variation occurs in the setal 
arrangement of these segments than in the prothorax would seem to sup- 
port Fracker’s contention that the condition in this respect is more primi- 
tive in the latter. The setal pattern of the mesothorax and metathorax, 
however, is on the whole very uniform. 

The arrangement of the setae of abdominal segments 1 and 2 differs 
essentially from that of the other segments only in the region where larva- 
pods are borne on the following segments. The setae which are normally 
borne on the larvapods on segments 3, 4, 5, and 6 are present on this portion 
of segments 1 and 2. The other setae of these two segments will be con- 
sidered later in the general treatment of the abdominal setae which follows. 
On segment 2 tau is apparently always well developed, but it has been found 
on segment 1 only in the Catocallinae, Phytometrinae and Hypeninae. 
Fracker figures it in the first abdominal segment of Feltia gladiarza, 
although the author has failed to find it in an abundant supply of material 
of this species. Omega, on the other hand, which is omitted from his 
figure, is apparently always present in the family on this segment, although 
very minute. The presence or absence of tau is the most fundamental 
character discovered in our entire study of the morphology of the noctuid 
larvae, making it possible apparently to separate two large groups of sub- 
families on this basis. The position of omega varies considerably in a 
transverse direction according to the genus, its minute size, however, 
renders it inadvisable to use this variation in tables. Some difference in 
longitudinal location is offered by sigma, which ranges from a position on 
the transverse line through pi to one distinctly caudad of it. The Cato- 
calinae apparently differ from other subfamilies in having the line nu-mu 
longer than the line pi-mu on segments 1 and 2, the opposite condition 
being distinctly present in all other larvae examined. On both these 
segments, in those subfamilies where it occurs, tau varies both longi- 


32 ILLINOIS BIOLOGICAL MONOGRAPHS [274 


tudinally and transversely, furnishing good generic characters through- 
out the family. It may be nearer to pi or to sigma and varies from a point 
on the transverse line through nu to one just cephalad of the transverse 
line through pi. 

Only one of the minute setae xa and xb is usually present on the abdomi- 
nal segments, altho both are found in Chloridea armigera and frequently 
the persisting seta is associated with a minute spot, which evidently repre- 
sents the vestige of the other. The transverse variation in the location of 
xa with reference to alpha and beta affords some phylogenetic indications, 
altho the minute size of xa precludes the use of its variations in tables. 
Typically this seta is further dorsad of beta on segment 1 than on segments 
2 to 7 inclusive, being most ventrad of all on segment 8. This variation 
involves the migration of beta as much as that of xa. Two genera examined, 
Catocala and Xylina, afford exceptions to the rule, xa being further dorsad 
relative to beta on segment 8 than on 1. In all other groups investigated 
xa is ventrad of the longitudinal line through beta, whereas in these two 
genera it is much dorsad of this line, an instance of parallel development. 

The difference in the longitudinal position of the spiracle with reference 
to the surrounding setae on successive segments in the individual follows a 
certain definite plan throughout the family. On segment 1 the transverse 
line through rho ranges according to the group from a position distinctly 
cephalad to one a little caudad of the spiracle. Rho is clearly further 
cephalad in segments 2 to 6 inclusive than in 1, its transverse line passing 
cephalad of the spiracle or tangent to the cephalic margin. Segment 7 
presents approximately the condition found in segment 1, the seta being 
further caudad than in segments 2 to 6, and ranging from a situation 
cephalad of the spiracle to one caudad of it. Two exceptions to this general 
plan have been noted. In Sidemia devastatrix the condition on segments 
1 and 7 does not differ clearly from that in the intermediate segments and 
in Papatpema nebris segment 7 exhibits the same location which it occupies 
on segments 2 to 6, segment 1 differing from the rest as usual. The fact 
that segments 1 and 7 show much greater variation in this respect than the 
intermediate segments indicates that the condition found on segments 2 to 
6 is the more primitive. Evidently in segments 1 and 7 the spiracle has 
migrated cephalad of its primitive position. In some cases this process has 
proceeded further on segment 1 and with other species on segment 7. The 
condition on segment 8, where the position of rho varies according to the 
group from a location cephalad to one caudad of the spiracle, reveals no 
uniform relation to that on other segments. Altho these minor variations in 
the longitudinal situation of the spiracle offer points of morphological interest 
they usually do not lend themselves readily to taxonomic application. The 
Catocalinae, however, apparently differ from all other groups within the 
family in having rho distinctly cephalad of the spiracle in segment 1. 


275) NOCTUID LARVAE—RIPLEY 33 


The spiracle has also migrated in a transverse direction, as indicated by 
its position with reference to the surrounding setae. In general it is further 
ventrad on segment 1 and further dorsad on segment 8 than on segments 2 
to 7 inclusive. Sometimes segments 7 and 8 present the same condition, 
as in Scolecocampa liburna, which is to be regarded as a specialization, since 
segment 7 as well as segment 8 has departed from the primitive arrange- 
ment. In Sidemia segment 8 does not differ in the transverse position of the 
spiracle with reference to epsilon from segments 2 to 7, as it does in the 
other genera examined. This may be reasonably considered as a generaliza- 
tion. 

From this consideration of the position of the spiracle it appears that 
segments 2 to 6 inclusive present the primitive condition, the spiracle 
having migrated cephalad on segments 1 and 7 and either cephalad or 
caudad on segment 8 depending on the group. It has, moreover, shifted 
ventrad on segment 1 and dorsad on segment 8, remaining usually in the 
same transverse position on segment 7 as on segments 2 to 6. 

The taxonomic value of the transverse variation of kappa in cater- 
pillars was early demonstrated by Dyar. Altho the situation of this seta 
offers no conspicuous differences in this family, it varies sufficiently to 
provide some generic characters. It is usually much further ventrad of the 
spiracle on segment 7 than on other segments. Achatodes zeae again affords 
an exception, having kappa further ventrad on segment 8 than on segment 
7, the reverse usually being true. Differences in the location of eta and mu 
afford generic characters, especially on segment 7, where they vary both 
transversely and longitudinally. The transverse position of omega relative 
to pi and sigma varies considerably throughout the family, seemingly 
according to the genus. The very minute size of omega, however, unfor- 
tunately precludes the use of this character in a table. 

On segment 8 beta is typically much further dorsad than on the seg- 
ments cephalad of it, presenting a specialized setal arrangement. The 
longitudinal line through alpha may pass considerably above beta or a 
little below it, the latter more specialized condition being less frequently 
encountered. This character promises to be useful in the separation of 
genera and of larger groups. Pi varies transversely to some extent on 
segment 8 relative to mu and sigma, affording generic characters. 

With the exception of the anal one, segment 9 may reasonably be 
regarded as the most specialized segment with respect to setal pattern. 
Here the migration dorsad of beta has proceeded much further than on 
segment 8. The transverse location of alpha relative to beta and rho varies 
according to the group, altho presenting considerable individual variation 
in some species. Rho may be nearer either to alpha or to beta depending 
on the genus. The transverse line through kappa may pass either caudad or 
cephalad of pi, both of these setae varying somewhat in their situation 


34 ILLINOIS BIOLOGICAL MONOGRAPHS [276 


according to the group, altho they provide no convenient characters for 
use in tables. 

The setae of the anal segment, which probably represents the fused 
tenth and eleventh abdominal somites, cannot be definitely homodynam- 
ized with those of other segments. Alpha, beta, and kappa vary a little 
in relative position according to the genus or in some instances within a 
genus. Kappa is most commonly equidistant from the other two but may 
be distinctly nearer to beta or less often slightly nearer to alpha. Both 
extremes have been found within the genus Phytometra. The position 
of the setae on the lateral aspect of the anal larvapod is perhaps subject to 
more striking variation than any other group of setae on the trunk of 
noctuid larvae. An usually conspicuous sensorium, which McIndoo has 
described, also contributes to the taxonomic value of this region, varying 
considerably in situation relative to the setae. Eta may be nearer either 
to epsilon or to omega, furnishing a basis for the separation of genera and 
larger groups, altho occasionally showing specific variation. Scolecocampa 
liburna presents an exceptional position of the sensorium, which is distad 
of eta (Fig. 53). In all other species examined it is distinctly proximad of 
the setae. The sensorium, eta, mu, and tau are frequently arranged so as 
to form the points of a diamond, which varies considerably in relative length 
and width, according to larger groups. The line from the sensorium to tau 
is usually longer than the one from mu to eta, altho the reverse situation is 
sometimes encountered. Either mu or eta may be nearer to the sensorium, 
so that the diamond is often out of true. Mu varies in location with refer- 
ence to the lines epsilon-eta and omega-tau, being nearer to either one. All 
of these variations appear to apply chiefly to genera. 


LARVAPODS 


The general form of the larvapods of noctuid larvae (Figs. 50-53) is 
typical for the entire order. Asin a number of related families, the crochets 
are arranged in a mesoseries and are homoideous and uniordinal (Figs. 51, 
58) representing a supposedly specialized type which Dyar considered to 
have descended from the circular one found in Hepialus. They are operated 
by muscles which attach entad of a small usually heavily chitinized spot in 
the center of the distal end of the uropod. As shown in Figure 59 each 
crochet lies within a membranous invagination whose mesal edge bears a 
number of pointed membranous projections. These have not been pre- 
viously described, so far as known. Their function is problematical. The 
proximal end of each crochet is pointed and curved mesad, serving for the 
attachment of muscles. Since the larvapods represent embryonic abdomi- 
nal appendages which have persisted into postembryonic life, the terms 
proleg and false leg in general use are inappropriate. 


277) NOCTUID LARVAE—RIPLEY 35 


Altho the extent of variation in the larvapods of noctuids does not 
approach that which Goosen’s series of these appendages reveals in the 
entire order, they differ quite markedly in form, number, relative size, 
number of crochets, and amount of chitinization. The setal arrangement 
is practically uniform. As previously stated, from two to four pairs of 
median larvapods may be present, the first one or two pairs, which are 
located on the third and fourth abdominal segments, being absent in 
certain groups. In the Phytometrinae the two cephalic pairs are usually 
wanting, altho Hampson mentions one genus whose larvae have the full 
number. The Catocalinae exhibit a pronounced tendency toward the 
reduction of the first two pairs, which reaches its acme in Caenurgia, where 
they are entirely absent. The first pair only are generally lacking or 
without crochets in the Hypeninae. According to Hampson, the Eras- 
trinae also bear but three pairs of median larvapods, altho the larva of 
Chamyris cerintha, which was evidently unknown to him, has the full 
number, the first pair being as well developed as the rest. The larvae of 
other subfamilies of which material has been available for study are pro- 
vided with four pairs of median larvapods with the first two pairs usually 
not strikingly smaller than the others. In certain Phytometrinae the 
vestiges of the lost larvapods can be discerned as heavily chitinized small 
protuberances bearing the setae in about the same position which they 
occupy in the fully developed appendage. Epizeuxis lubricalis of the 
Hypeninae has the first pair fairly well developed but completely lacking 
crochets. The number and relative size of the larvapods furnish very 
fundamental characters, altho no noctuid subfamilies can be reliably 
diagnosed upon this basis alone. 

Since the caterpillars of the most generalized families and of the great 
majority of all Lepidoptera bear four well developed pairs of median 
larvapods, this is most reasonably regarded as the generalized condition. 
Their reduction has taken place in a few very distantly related groups, this 
process having proceeded to a different extent in each. In the Cochlidiidae 
they are entirely absent and in the Geometridae only the last pair of 
median ones and those of the anal segment persist. Certain groups of 
Noctuidae, apparently represent an incipient stage in this process of reduc- 
tion, as exemplified by the Agrotinae, in which the first two pairs are typi- 
cally somewhat smaller than the rest. In the Catocalinae the same ten- 
dency is exhibited to a much greater degree. The Phytometrinae and 
Hypeninae, whose larvae are generally the most highly specialized in the 
family in this respect, are placed by Hampson among the most specialized 
noctuids on the basis of the structure of the adults, whereas the larvae of 
the Acronyctinae, which he regards as a relatively generalized subfamily, 
always have the full number of larvapods well developed. 


36 ILLINOIS BIOLOGICAL MONOGRAPHS [278 


There appears to be no very definite correlation within the family between 
the mode of life and the loss or reduction of the first two pairs of larvapods, 
although this condition is accompanied by the habit of walking with a 
looping gait and of moving more rapidly, a point to be discussed in connec- 
tion with the postembryology of the larvapods. The lengthening, however, 
of the two latter pairs of median and of the anal ones, which is so pro- 
nounced in larvae of Catocala, appears to be a modification for arboreal 
life. The same specialization is found to a lesser degree in many arboreal 
caterpillars. This type of larvapod seems to be found only in larvae that 
climb extensively. The fact that the development of this modification has 
proceeded further in the catocalas than in most other arboreal larvae is 
consistent with the occurrence in this genus of a number of marked adapta- 
tions to life in the tree stratum of the deciduous forest. The eggs, larvae, 
and adults are protectively colored like the bark of the trees on which they 
rest. Practically all of the species feed upon the foliage of deciduous trees 
or upon plants of the deciduous forest. 

The number of crochets is larger in Catocala than in most noctuid 
larvae, which is apparently a further specialization for climbing on the 
trunks and twigs of trees. From the first to the anal pair of larvapods 
respectively the number of crochets in Catocala grynea is 30, 36, 43, 55. 
The other extreme is presented by some of the subterranean forms, Feltia 
gladiaria having 8, 12, 14, 14, 18 and Sidemia devastatrix 12, 14, 14, 14, 14. 
In general the anal pair has the largest number and the first pair often 
bears a few less than the others. The formula for Cirphis phragmitidicola, 
22, 24, 26, 30, represents an average one for the family. Some individual 
variation occurs in this respect, the number varying two or three each way 
from the mean. It is frequently different on the two sides of the same 
individual, as Dampf has shown it to be in the psychid, Eumeta. Con- 
siderable difference in the number of crochets is sometimes exhibited by 
closely related species, Polia meditata having 16, 18, 18, 20, 26, and renigera 
12, 12, 16, 18, 19. These two species are decidedly subterranean. The 
closely related Ceramica picta, on the other hand, which enters the soil only 
to pupate, frequently climbing shrubbery to feed, has 26, 27, 30, 32, 35. 
Beyond the presence of a larger number in the arboreal forms, there appears 
to be no marked correlation between the mode of life and the number of 
crochets, altho the smallest number is apparently best represented among 
species which burrow in the soil. Specific determinations may often be 
facilitated by these formulae, altho a considerable difference in this respect 
according to the instar necessitates a positive knowledge of the stadium 
before applying this character. 


279] ; NOCTUID LARVAE—RIPLEY aT 


POSTEMBRYOLOGY 


Ecdysis is undergone by noctuid larvae four, five, or six times, depend- 
ing chiefly on the species, but somewhat on other factors. They present, 
then, five, six, or seven stadia. After each molt the postembryonic changes 
which have taken place during the previous stadium are suddenly revealed. 
These changes may be highly conspicuous, but are more often so very slight 
that careful observation or accurate measurement is necessary to detect 
them. Before considering the structural changes undergone in larval 
postembryology, we shall discuss at this point the significance of the 
number of stadia, and of the amount of increase in size from one stage to 
the next. 


NUMBER OF MOLTS 


Although not absolutely fixed, the number of molts characteristic for 
species of lepidopterous larvae is not subject to the considerable variation 
found in some other orders. Wodsedalek, for example, greatly increased 
the number of stadia in the larvae of Trogoderma (Dermestidae) by star- 
vation. It is certain that environmental factors may at times cause one 
molt more or less in certain lepidopterous larvae. Payne found that those 
of Ceramica picta pass but five stadia in both generations in Nova Scotia, 
whereas those reared in Illinois by the author have uniformly undergone 
one molt more than these northern individuals. Hibernating butterfly 
larvae have been known to molt once more than those of the summer broods. 
This phenomenon has not been found in the noctuid larvae, A grotis c-nigrum 
and Polia renigera, which have been reared through both winter and sum- 
mer broods. Weniger reduced the number of stadia in Eacles imperialis 
and Antheroca mylitta from the normal six to five, by rearing them at about 
25 degrees C. coupled with high humidity. By rearing the cutworm, 
Agrotis ypsilon, at 21 degrees C.., 100% humidity, and at 28 degrees C., 
100% humidity, in ventilated j care the author has similarly decreased He 
normal number of molts by one. It is a curious fact that the cutworm, 
Polia renigera, adds one stadium to its usual number when reared under 
these same conditions, being affected in an opposite manner by the same 
stimulus. 

Sexual differences in the number of stadia were first recorded by C. V. 
Riley in Hemerocampa leucostigma, the males always molting four times, 
the females either four or five. Payne has recorded the same phenomenon in 


38 ILLINOIS BIOLOGICAL MONOGRAPHS [280 


a few other members of this family (Liparidae). This peculiar condition 
has been observed by the author in but one noctuid species, Caenurgia 
erechtea. Its significance will be discussed later. 

Besides these environmental and sexual variations in the number of 
stadia, there are very probably hereditary tendencies toward individual 
differences in this respect. Davis records one individual of Cirphis uni- 
puncta passing seven stadia instead of the usual six. Since this exceptional 
individual was reared under the same conditions as hundreds of others, it 
seems evident that heredity and not environment must account for this 
exceptional instance, the possible significance of which will be considered 
later. Similarly, one larva of Agrotis ypsilon, reared with fifty-two others, 
molted but six times instead of seven, according to our records. 

In 1890 Dyar called attention to the fact that the widths of the success- 
ive heads of any lepidopterous larva in all its stages bore a certain definite 
relation to each other. His presentation of this point may be summarized 
as follows: the quotient obtained by dividing the width of the head of any 
instar by that of the previous one is a constant, which is characteristic 
for the species. This principle has been termed Dyar’s Law. Its utilitar- 
ian value is obvious, enabling one to determine what instar he is dealing 
with when a specimen or a published measurement of any other known in- 
star is available. A fair indication as to the number of stadia may also be 
obtained if the size of the first and of the last instar is known. 

An inspection of a large number of species will reveal the condition in 
this regard within the Noctuidae. Although the measurements represent - 
averages derived from the number of individuals indicated, in many cases 
a much larger number has been examined to insure the determination of 
a fair average, as well as to find the extremes of variation. The material 
studied was either preserved when collected or grown under approximately 
natural conditions. Individual variation in size is not as great as might 
perhaps be expected, usually rendering the identification of instars a 
simple matter. The figures expressing the percentage of variation are ob- 
tained by dividing the maximum variation found, by the average, multi- 
plying by 100, (to express as percentage) and dividing by 2, so that the 
deviation from the mean in either direction, not in total, is represented. 
The later instars naturally present the greatest variation, having been 
longer subject to external influences. Where the measurements are based 
on individuals of different broods the variation is usually larger than other- 
wise, since the larvae of certain generations often grow larger than those of 
others in an ordinary season. All measurements have been made with an 
ocular micrometer. 

The inconstancy of Dyar’s supposed constant, which we will refer to 
as the index of growth, is striking, varying in Agroftis ypsilon, for instance, 
from 1.28 to 1.84. The average for any particular species ranges from 1.44 


281} NOCTUID LARVAE—RIPLEY 39 


to 1.61. The increase from first to second stadia is usually greater, from 
penultimate to last more often less than for other molts, this latter condi- 
tion being explainable by the fact that the more rapid development of 
adult structures in the later instars leaves proportionately less energy 
available for growth. The other noticeable differences in indices of growth 
within a species present no uniformity. In one species, for instance, the 
index from second to third stadia is greater than from third to fourth, in 
another the reverse may be true, or in a third species these indices may be 
equal. The question must arise, then, as to whether the relation between 
these different indices within a species be definite to any extent. 

An examination of the successive exuviae of isolated individuals, shows 
us that the variations in the index of growth for any species are of no uni- 
formity, with the exception of the tendency toward largeness of the first 
and smallness of the last. All other variations are to be accounted for, 
then, by environment, all indices but the first and last probably tending to 
be equal under uniform external conditions. Any influences affecting the 
rate of activity of the moulting mechanism differently from that of the 
general metabolism must necessarily either increase or decrease the index 
of growth. Thus, if growth be impeded without interfering proportionately 
with hypodermal activity, or at least with the molting mechanism, a small 
index will result. Wodsedalek, by starving larvae of Trogoderma (Der- 
mestidae), obtained many exuviae, some of the last of which were actually 
smaller than the earlier ones. In like manner factors favoring growth more 
than molting necessitate a large index. 

The effect of external factors on the index is characteristic. Starvation 
and parasitism, of course, greatly reduce growth, but do not retard the 
molting processes proportionately, since the number of stadia is not affected, 
larvae continuing to molt when very little growth is undergone. Favorable 
climatic factors, on the other hand, increase the index. The unusually 
large increase from second to third stadia in Agrotis ypsilon is to be ex- 
plained by the fact that the individuals upon which the given figures are 
based were reared simultaneously under like natural conditions, which were 
evidently optimum for growth, or nearly so, while these individuals were 
passing the second stage. 

We have demonstrated the fact that some species increase in size from 
first to last stages considerably more than others, the total amount of 
growth being characteristic for the species, although variable according to 
external factors. It may vary widely in closely related species as in 
Lycophotia margaritosa and infecta. Although molting has been generally 
considered to be primarily a phenomenon necessitated by growth, some 
entomologists have been inclined to question this point, tending rather 
to emphasize its excretory significance. It is to be noted, however, that 
the seven-staged species grow more than the six-staged. This obvious 


40 ILLINOIS BIOLOGICAL MONOGRAPHS [282 


correlation between the total growth index, obtained by dividing the width 
of the head of the last instar by that of the first, and the number of molts 
lends weight to the former more general view. In Caenurgia, moreover, 
where there is a sexual difference in the number of stadia the females, 
which often molt once more than the males, average larger in size, The 
number of individuals of this species used in Table II is too small to justify 
our drawing conclusions from the fact that the growth index of the males 
exceeds that of the females. The fact that Cirphis unipuncta, which pre- 
sents the greatest total growth index of the six-staged species, has been 
known to pass seven stadia in one instance, is of especial interest in this 
connection. 

It follows mechanically that species with a large total increase, in other 
words, those with a first instar whose head is proportionately small for that 
of the last instar, produce eggs relatively small for their adults, the small 
first instar being correlated with a small egg, and the large last instar pro- 
ducing naturally a large moth. The egg measurements in Table I have 
been made from alcoholic specimens and are, therefore, somewhat larger 
than certain corresponding published measurements based on fresh eggs. 
The figures given represent the diameter of the largest circumference, the 
periphery of the typical noctuid egg being circular. In those species whose 
eggs have one diameter slightly greater than the one at right angles to it, 
an average has been given. Altho the correlation between egg-diameter 
and the width of the head of the first instar is clearly demonstrated in 
Table I, the ratio between these two measurements varies considerably 
according to the species. Ceramica picta presents an extreme condition 
where the egg is small relative to the larval head, the ratio being 1.65. In 
the catocalas, on the other hand, we find the width of the egg proportionate- 
ly large for that of the larval head, the ratio reaching 2.62 in C. illia. This 
condition may possibly bear a direct relation to the habit of hibernation in 
the egg, which is general in this genus. 

The shape, as well as the general internal structure of the abdomen of 
all noctuid moths is very nearly uniform, approximately the same propor- 
tional amount of space being used for egg-carrying in all species. It follows, 
therefore, that a moth producing eggs proportionately small for its size 
must bear a larger number than one whose eggs are large relative to the 
size of the adult. We should remember when considering this point that 
the moths of this family have but a short period for oviposition, usually 
laying all their eggs in a few successive nights, which permits of no egg- 
development during the life of the adult, such as occurs in the queen bee. 

The data for the fecundity is based upon the number of fully developed 
eggs in the abdomens of reared moths and represents potential fecundity. 
Since the number of eggs actually laid in breeding cages is determined by 
external stimuli, all eggs in the abdomen being oviposited only under opti- 


283] NOCTUID LARVAE—RIPLEY 41 


mum conditions, which for many species are difficult to obtain artificially, 
the published records of the number of eggs laid by various species are un- 
reliable as indices to the potential fecundity. The undeveloped eggs, which 
are never laid, occupy a quite uniformly small space in the abdomen. Ac- 
curate data on fecundity can be obtained only with difficulty, since counts 
must be made of the eggs contained in the abdomens of moths emerging in 
captivity only. Moreover, a large number of individuals should be exam- 
ined, because of the great individual variation in this respect. In spite of 
the regrettable insufficiency of data, the column headed potential fecundity 
presents significant indications. 

A consideration of the mechanical relations already discussed enables 
us to understand the significance of the correlation between high fecundity 
and large total growth. Although a general relation between these con- 
ditions is clearly indicated, we note that certain irregularities occur. Feliza 
subgothica and Ceramica picta lay an exceptionally large number of eggs 
relative to the amount of their larval growth. An examination of the ratios 
between the diameter of the egg and the width of the head of the first in- 
star in these two species reveals the fact that both bear eggs proportionate- 
ly small for the size of their first instars. This condition enables the moths 
to lay a large number of eggs relative to the amount of larval growth for 
the species, accounting for the irregularity in the correlation. The relation 
between fecundity and growth is not direct, since the former increases 
more rapidly than the latter, as is evident when we read from top to bottom 
in these columns, a relatively slight increase in growth corresponding to a 
large increase in fecundity. It is highly probable that the factors determin- 
ing fecundity are many. Of these factors the amount of growth is an im- 
portant one in this family. 

It should be noted that Cirphis unipuncta, with the largest total growth 
index of the six-staged species, having seven stadia rarely, attains the 
highest fecundity of those with six stadia. This destructive species has 
three broods in Illinois. The larvae developing in June grow markedly larg- 
er than those of the following brood, which pass the larval period in mid- 
summer, the individuals of the fall-brood being nearly as large as those of 
the spring-generation. This relation probably holds only for the latitude 
and climate of Illinois in a usual season. Since the eggs of all generations 
are of the same size, the total growth is different for each brood under 
normal weather conditions. Altho our data as to the fecundity of the 
moths of different broods is inadequate, it seems quite evident that those 
developing from the large September larvae must have relatively high 
fecundity. This is suggested as a factor contributing to the fact that the 
spring-larvae, offspring of moths from the September larvae, almost al- 
ways constitute the brood which attains such great numbers in Illinois, 
accompanied by the well known army-worm devastation. Altho the larvae 


42 ILLINOIS BIOLOGICAL MONOGRAPHS [284 


of this brood also attain a large size, they become greatly reduced in num- 
bers by wilt disease and parasites, so that the midsummer -brood is usually 
not large. The small individuals of the midsummer-generation yield moths 
of low fecundity, accounting for the usual inconspicuousness of the third 
brood, altho infrequent outbreaks have been observed in September. It 
seems probable that this principle may prove to be an important one to be 
considered in the prediction of these outbreaks. 

The fact that fecundity is hereditary in animals has been well es- 
tablished. Geneticists have found that the tendency to bring forth twins 
and triplets is hereditary in mammals. By artificial selection, Pearl and 
Surface have greatly increased the egg-laying propensities of a certain 
strain of Plymouth Rock fowls. It has been well established that fecundity 
in Drosophila is an hereditary trait. Individual variation in fecundity is 
considerable within the Noctuidae. Since those strains, in a species of 
this family, with a tendency to lay many eggs must transmit this trait to 
many more individuals than would those inclined toward low fecundity, 
it seems evident that in general species must increase fecundity in the 
course of evolution up to a point where it is checked by some sort of barrier, 
mechanical or physiological. The only possibility for a non-prolific strain 
to untimately persist would involve necessarily its accompaniment by in- 
heritable, advantageous properties not possessed by prolific strains, such 
advantages offsetting their low fecundity. We have no evidence indicating 
that this latter, seemingly unlikely possibility has taken place within the 
Lepidoptera. 

In the light of the correlations demonstrated, it seems evident that the 
amount of growth, or the number of molts, would act as a barrier to an 
increase in fecundity, furnishing mechanical limits, which would prevent 
further expression of this tendency. An hereditary increase in the number 
of molts, such as the one cited with regard to a single individual of Cirphis 
unipuncta, would allow the individuals possessing this trait to attain a 
larger size and consequently a higher fecundity. This would, therefore, 
be transmitted to a larger number of offspring than would the tendency 
toward a lesser number of molts. The persistent variation, then, would be 
the one with the largest number of stadia. 

On the basis of this theory, the largest number of larval stages is the 
most specialized condition in this family. This conclusion is supported by 
all the other evidence available. As shown by Dyar, the great majority 
of lepidopterous larvae undergo ecdysis four times, five times frequently, 
and three, six, seven, eight, nine or ten times rarely. According to our 
data the molting five times appears to be the general condition throughout 
the Noctuidae, four molts occurring only in the two species of Phytometra, 
and in the male of Caenurgia erechtea, and six being found in but three 
species. We should be justified apparently in regarding the passing of 


285) NOCTUID LARVAE—RIPLEY 43 


seven stadia as a specialized condition, merely on account of its exceptional 
occurrence. 

Since the two species of Phytometra, brassicae and biloba, which have 
been reared through all larval stadia by the author, present but five 
stadia and contexta, according to Thaxter, passes six, it would seem that 
this biological character is not a fundamental one. The persistence 
of the generalized condition of molting but four times in this structurally 
specialized group is parallelled by the situation found in Hepialus, whose 
moth is very generalized structurally, but whose larva has developed the 
specialized habit of root-boring. 

In Caenurgia erechtea the number of stadia presents an interesting 
secondary sexual character, the larva undergoing ecdysis but four times in 
the male and four or five in the female. The males of this species offer the 
only instance known to us outside of the Phytometrinae where a noctuid 
larva molts but four times. Parallel instances have been found by C. V. 
Riley in Hemerocampa leucostigma and by Payne in other liparid larvae, 
in which the male passes five stadia and the female either five or six. This 
phenomenon is most probably to be explained by the fact that the female 
larvae generally attain a larger size than the male. The fact that the 
female varies in the number of molts indicates further that the larger 
number of stadia represents the more specialized condition. 

The species passing seven stadia, A grotis ypsilon, Lycophotia margaritosa 
and Nephelodes emmedonia, do not constitute a phylogenetic unit, but have 
developed an extra molt independently, since each is more closely related 
to different six-staged groups than they are to each other. Lycophotia 
infecta undergoes ecdysis but five times. Specific differences in this respect 
in the genus Phytometra have already been mentioned. 


POSTEMBRYONIC CHANGES 


A study of the postembryology of noctuid larvae, as well as a consider- 
ation of the ontogeny of animals in general, convinces us that the structural 
changes exhibited in ontogeny are not all an expression of the same biolog- 
ical factor, but are of a number of distinctly different kinds. The structural 
changes appearing in the postenbryonic development of caterpillars may 
be conveniently classified as follows:- (1) Recapitulative; (2) Non-recapit- 
ulative; (a) Adaptive to unequal function; (b) Necessitated by the me- 
chanics of growth; (3) Compound; (a) Recapitulative-adaptive; (b) Recapit- 
ulative-mechanical; (c) Adaptive-mechanical. 

The Law of Recapitulation is of quite general but by no means of uni- 
versal application, ontogenetic sequences which do not conform to the law 
being many and well known. The fact that a mammal at birth has a head 
large relative to the size of its body does not lead us to regard the ancestor 


a ILLINOIS BIOLOGICAL MONOGRAPHS [286 


of this animal as the possessor of a proportionately large head. Nor does 
our knowledge of the postembryology of the house-fly convince us that it 
descended from an apodous insect with vestigial biting mouth-parts. We 
do not look to recapitulation to account for such conditions. Such post- 
embryonic changes may be described as non-recapitulative as opposed to 
those of recapitulative significance, which apparently conform to the law. 
This point can be determined with regard to a structure undergoing change 
in ontogeny with a certainty proportional directly to our knowledge of the 
phylogeny of the structure in question. Thus, if the changes undergone 
by any structure in the course of its development recapitulate its race- 
history, we regard that structure as of recapitulative significance, but if 
its phylogeny be doubtful, our decision on this point must be proportion- 
ately tentative. The successive instars of species of Leucaspis figured by 
Lindinger reveal beyond any reasonable doubt the recapitulative signifi- 
cance of the pygidial structure in these coccids, the postembryology re- 
capitulating minutely their phylogeny, which has been well established by 
the extensive morphological studies of MacGillivray. The recapitulative 
significance of wing-venation in pupal postembryology has already been 
mentioned. Of many parallel instances the case of Mantispa is perhaps 
the most familiar, the larva of this insect passing through transitional 
stages from a thysanuriform to an eruciform type, repeating the generally 
accepted phylogeny of the latter form of larva. The taxonomic advantages 
gained by the establishment of the recapitulative significance of a structural 
change in postembryology will be demonstrated later. 

Many structures are adapted to the mode of life of a particular stage 
or to a habit associated with a single point in the life-cycle. Such organs 
function unequally or even differently in different stages of development, 
frequently being used in only one stage. Lepidopterous pupae, notably 
of the Sesiidae, frequently bear spines or projections used for breaking 
the cocoon and for wriggling into the open. These belong distinctly to the 
pupae. A parallel instance is furnished by the wings of insects, which 
function only in adults and appear in earlier stages merely as developing 
adult structures. Similarly caterpillars often spin silk in certain stadia 
and not in others, and noctuid larvae frequently do not employ the first 
one or two pairs of larvapods in the first stadium. This unequal function 
of a structure in different stages is generally correlated with structural 
differences, hence a non-recapitulative factor is introduced. Postembry- 
onic changes which are the expression of this factor will be referred to as 
adaptive to unequal function. It is evident that the two factors, recapitu- 
lation and adaptation to unequal function may act in the same or in opposite 
directions with reference to a particular postembryonic change. In the 
former event it is impossible to ascertain to what extent each of these forces 
has operated in the production of the change, which is consequently most 


287] NOCTUID LARVAE—RIPLEY 45 


reasonably regarded as the expression of the two factors combined and is 
referred to as recapitulative-adaptive. When these two forces conflict, 
the effect of the recapitulative one is completely obscured, as will be demon- 
strated later, the factor of adaptation to unequal function being dominant. 

Since certain animal structures do not grow as rapidly as others, they 
are generally relatively larger in earlier developmental stages than in later. 
The familiar instance already cited of the newly born mammal, with its 
proportionately large head, is parallelled generally by insects, the heads 
of the first instar being markedly large relative to the body. The ocellariae 
and crochets of lepidopterous larvae are strikingly large in the first instar, 
growing slowly in comparison with the surrounding structures. These 
phenomena are obviously not an expression of recapitulation, but are most 
probably to be explained by the relative rates of cell proliferation in differ- 
ent kinds of tissue. This factor, like unequal function, may undoubtedly 
operate either with or against the recapitulative force. When\the effect 
of the latter is obscured by that of the mechanics of growth, the resulting 
change is classified as mechanical, whereas when these two forces exert 
themselves in the same direction the change produced would be termed 
recapitulative-mechanical, although no clearly defined instance of this 
situation has been found. 

The compound types involving recapitulation have been already de- 
fined. One instance noted is obviously the result of a combination of un- 
equal function and mechanics of growth. This change is classified as 
adaptive-mechanical. 

Of the possible combinations of these factors all have been actually 
indentified as responsible for certain postembryonic changes in noctuid 
larvae, except two, recapitulative-mechanical and recapitulative-adaptive- 
mechanical. The first of these very probably finds expression in the mi- 
gration of certain head-setae to be discussed later. The second type of 
change possibly occurs also in these larvae. 

It should be noted that, unlike the other two factors, recapitulation is 
to be regarded as a general law, which fails to express itself only when ob- 
structed by other forces, which are dominant over it. 

Many postembryonic changes in structure are inexplainable in the dim 
light of our knowledge of the factors involved. Our lack of adequate 
knowledge of phylogeny is probably largely responsible for this situation, 
since many changes such as those of the head-capsule of muscid larvae 
figured by Nielsen, may prove to be of recapitulative significance, when 
sufficient morphological work is done to establish the race-history of such 
structures. An investigation, moreover, of the functions in different stages 
of organs undergoing postembryonic changes will most probably reveal 
many instances of adaptation to unequal function, while the determination 
of the importance of the factor of the mechanics of growth awaits the re- 


46 ILLINOIS BIOLOGICAL MONOGRAPHS {288 


searches of the histologist. Hence morphological, biological and histolog- 
ical investigation may be expected to explain for the most part these num- 
erous problematical changes, such as those in the shape of the body-setae 
and of the antennae of caterpillars, in the number of facets in the eye 
of the nymphs of dragon-flies, in the heads of muscid larvae, in the struc- 
tures of the caudal end of the body of tipulid larvae, in the number of tarsal 
segments in the Heteroptera, and many others. Such investigations will 
probably reveal a number of types not listed in our present classification, 
which is necessarily very restricted, applying only to noctuid larvae. 

The postembryology of the fixed parts of the noctuid larval head reveals 
the following changes: 

(1) Appearance of the adfrontal sutures; (2) Change in the relative 
length of the epicranial stem; (3) Mesal extension of the postgenae; 
(4) Change in the shape of the labrum; (5) Reduction in the relative size 
of the ocellariae and sensoria; (6) Change in the position of the setae; 
(7) Change in the shape of the setae; (8) Change in the coloration. 


ADFRONTAL SUTURES 


Although the presence of the adfrontal sclerites has long been regarded 
as a condition diagnostic for lepidopterous larvae, the fact that this area 
appears only in the later stadia, at least in noctuid larvae, has apparently 
not been discovered. Very frequently the coloration of the early instars 
gives the appearance of adfrontal sclerites where no structural differentia- 
tion exists, which has most probably been conducive to the general over- 
looking of the true situation. In the noctuids these sutures are distinct 
only in the larvae of the two later stadia, very faint indications being some- 
times distinguishable in exuviae or treated heads of the third from last 
stage. The adfrontal sclerites have been regarded as bearing a direct 
structural relation to the infoldings along the epicranial arms. Fracker 
speaks of them as the “external expression of the attachment of the 
anterior arms of the tentorium.”’ An inspection of a section thru this 
region (Fig. 1) reveals absolutely no connection between the adfrontal 
suture and the epicranial parademe, to which the pretentorium is attached. 
This suture appears externally as a narrow light-colored line constant in 
general position throughout the family but varying much in its irregular 
curving, even within a species. In sections it is not distinguishable from 
the general cuticle, except by its lighter pigmentation. Since the older ideas 
of its significance are obviously incorrect, our present problem is to account 
for its existence. 

The usual place of splitting in the head-capsule at molting and at pupa- 
tion is along the epicranial stem and arms in all but the more specialized 
forms such as dipterous or coccinellid larvae or coccid nymphs. We regard 
this, therefore, as the generalized condition in insects. As was stated in 


289] NOCTUID LARVAE—RIPLEY 47 


our consideration of the morphology of the tentorium, the great reduction | 
of this originally supporting structure has been accompanied by the 
development of a number of deep infoldings, one of which occurs along the 
epicranial suture. As might be expected, the marked specialization in this 
region is accompanied by a specialized condition in molting, the entire 
head-capsule being shed intact. So far as we know the larvae of no other 
order molt without breaking the exuvia of the head, altho some nymphs do 
so. It seems probable that the deep infolding along the epicranial suture 
has rendered the usual splitting impossible. The great change in form 
undergone at pupation, however, makes a break in the last head-capsule 
mechanically necessary. This occurs along the epicranial stem and 
adfrontal sutures. So far as we have been able to determine they have no 
other function. These structures are to be regarded, then, as a modification 
for pupation due indirectly to the greatly reduced condition of the ten- 
torium and to the deep parademe along the epicranial suture, which has 
taken over the supporting function of the tentorium. 

The well developed condition of these sclerites in the next to the last 
instar, where they do not function, is paralleled by the general occurrence 
of adaptive structures in stages earlier than the one in which they are used. 
Altho the adfrontal sutures appear in larval development as they pre- 
sumably did in phylogeny, beginning as a very faint line which becomes 
prominent later, the fact that they function only in the last instar indicates 
that the factor of unequal function also plays an important part in their 
development. If recapitulation alone were operating on this postembry- 
onic change, we should, moreover, expect these sutures to appear in the 
first instar, as shown by the following facts. Their universal occurrence 
throughout the order indicates very strongly that they were present in the 
ancestral lepidopterous larva. Since the first instar of the noctuid larva is 
typically noctuid, it presumably represents with reference to recapitulation 
a period in phylogeny later than the one in which the Noctuidae appeared, 
certainly much later than the period in which the adfrontal sclerites 
originated. Hence on the basis of recapitulation alone the first instar would 
exhibit well developed adfrontal sutures. Their failure to appear until late 
in larval development is evidently due to the fact that they function only 
in the fully grown larva. This postembryonic change is evidently the 
expression of the two factors recapitulation and unequal function and is to 
be classified as recapitulative-adaptive. 


EPICRANIAL STEM 


As has already been shown in our consideration of the morphology of the 
head, the relative length of the epicranial stem varies widely in the larvae 
of this family, (Figs. 2, 15, 16, 17) furnishing a character second only to 
the number of larvapods in conspicuousness. The proportional length of 


48 ILLINOIS BIOLOGICAL MONOGRAPHS [290 


this suture is most conveniently expressed in terms of its ratio to the length 
of the front. The quotient obtained by dividing the length of this sclerite 
by that of the epicranial stem will be referred to as the epicranial index 
and expressed by F/Ep. The great majority of lepidopterous larvae have a 
fairly long epicranial stem, Types 4 and 5 predominating. Type 5, with the 
epicranial stem longer than the front, occurs more frequently than Type 4, 
with the front exceeding the stem in length, in the Noctuidae and their 
allies, as well as in the Sphingidae and Rhopalocera. The average epi- 
cranial index normally found in the Noctuidae is about 0.7, the stem being 
somewhat longer than the front. Within the great superfamily Noctuoidea, 
the markedly short epicranial stem occurs only in certain genera of the 
Noctuidae. This condition is very frequently seen, nevertheless, since 


Hypothetical figures showing the relation of the front and epicranial stem. adf, adfrontal 
sclerite; cc, cervacoria; ea, epicranial arm; es, epicranial stem; f, front. 


many of our commonest and most economically important noctuid larvae 
present this type of head. The infrequent occurrence of the reduced epi- 
cranial stem in the Noctuidae and allied families indicates that this is a 
specialized condition, at least in this group. 

Moreover, wherever found in lepidopterous larvae, the short epicranial 
stem is associated with a specialized feeding-habit, that is, a habit other 
than the usual leaf-eating one, which we may reasonably attribute to the 
ancestral lepidopterous larvae, on the basis of its general occurrence in 
existing forms. Similarly, the parasitic life of certain of the family Orys- 
sidae is to be considered as a specialized one, since the larvae of the horn- 
tails are typically borers. Leaf-mining larvae whether coleopterous, dip- 
terous, or lepidopterous furnish an instance of specialized habit. The root- 
boring habit of the larvae of Hepialus is to be regarded as a biological 
specialization, altho their adults are structurally generalized. The larva 
of the noctuid, Epizeuxis lubricalis, feeds upon dry dead-wood, that of 
Scolecocampa liburna on moist dead-wood. Various cut-worms are sub- 
terranean to a greater or less extent. Each of these modes of feeding 


291) NOCTUID LARVAE—RIPLEY 49 


represents a departure from the leaf-eating habit and free-living existence, 
which were most probably characteristic of the ancestral lepidopterous 
larva. 

There is a correlation between the short epicranial stem and specialized 
feeding-habit. It will be seen that Types 1 and 2 occur only in leaf-miners, 
Type 3 being also confined to larvae of this habit except in the seed-eating 
or stem-boring Prodoxidae, in the wax-eating bee-moth larvae, and in the 
leaf-rolling Tortricidae. Similarly in the Noctuidae the reduced epicranial 
stem is always associated with a specialized habit, the subterranean mode 
of life. The more pronounced this habit the shorter is this suture. 

It has been necessary in order to establish this correlation to find criteria 
by which we may compare larvae of various species with reference to their 
subterranean proclivites. Cut-worms have generally been described in 
economic literature as larvae which hide beneath the ground by day, eating 
at or beneath the surface during the night. Our experiments have shown, 
however, that there is considerable diversity of feeding-habit, even within 
this biological group. Certain so-called cut-worms never enter the soil, 
others do so only under extreme stress, and some, on the other hand, never 
come above ground except for ecdysis. In addition to observations made on 
larvae reared under natural conditions, two series of experiments have been 
performed to determine the relative extent of the development of the 
subterranean habit with as many species of noctuid larvae as possible. 
The first of these determines which species are able to burrow into the soil 
and to what extent this ability has been developed in each. The second 
series of experiments determines the extent of the power to resist sub- 
mergence in water, a resistance which subterranean animals have generally 
developed. The combined results derived from these two lines of investiga- 
tion enable us to form a fairly accurate idea as to relative “‘subterranean- 
ness” of various species. We will now consider these experiments. 


DETERMINATION OF BURROWING HABIT 


The determination of the relative extent of the development of the 
power to burrow into the soil in the larvae of various species is the object of 
the first series of experiments. The logical method for making manifest 
an ability or tendency to burrow into the ground, however slight, involves 
the subjection of the organism to an irritating factor to which it reacts in 
a markedly negative manner, at the same time excluding all means of 
avoiding this factor except by entering the soil. Lepidopterous larvae 
generally avoid direct sunlight, a large proportion of them being nocturnal 
in habit. This is especially true of noctuid larvae, the cut-worms being 
notoriously active at night. Altho precise experiments on the reactions of 
these insects to light are much to be desired, anyone who has worked with 
them extensively will have noticed, without doubt, a generally marked 


50 ILLINOIS BIOLOGICAL MONOGRAPHS [292 


negative response to light. The author knows of no other natural factor 
calling forth such immediate and pronounced response. These experiments 
have been performed, therefore, in the following manner: 

An ordinary fifty watt electric light bulb was suspended above the 
center of a glass-jar three inches in diameter, containing soil, with the 
lowest point of the bulb six inches above the soil. A thermometer was sus- 
pended with its bulb touching the soil in the center of the jar. The typical 
black earth of Illinois was used in a finely pulverized condition and suffi- 
ciently humid to eliminate dust. It was packed down lightly on top, 
leaving an even surface. The temperatures ranged from 33.3 to 35.5 
degrees C. which was much higher than that of the laboratory due to the 
heat from the light. Except in Experiment 3 all material used was reared 
outside under approximately natural conditions and well fed. It was not 
brought into the laboratory until immediately before the experiment was 
to be started, except in Experiment 3. To avoid interference with one 
another, not more than five larvae were put together in the same jar. 
Frequently several instars of the same species were used, altho they always 
reacted alike, so far as could be observed. Observations were taken every 
few minutes, account being kept of the time required for the larvae to 
become visibly stimulated, as well as of the time elapsed before each 
individual should become buried, wholly or partially. These experiments 
were performed in April and May, except where otherwise indicated in the 
tables, consequently the temperatures to which the larvae were subjected 
during the experiments were unnaturally high, probably adding to the 
irritation produced by the light. 

It has been shown that stimulation is usually immediate. Well fed 
larvae, which lie motionless when brought into the laboratory from the 
outside, generally exhibit pronounced irritation as soon as subjected to the 
light, running rapidly about the jar. The phrase “‘time required for sub- 
mergence”’ expresses the time from the beginning of activity to the time 
when the individual is entirely or partially buried. In several instances 
certain individuals ceased activity as soon as the head and thorax were 
beneath the surface. This feature seems to be an individual rather than a 
specific trait. While the larvae of some species commence burrowing within 
two or three minutes after they become stimulated, entering the soil per- 
pendicularly and disappearing within a few seconds after they begin to dig, 
others crawl for half an hour, making an occasional abortive attempt to 
thrust their heads beneath the earth, finally very gradually burying them- 
selves by entering the soil at a small angle with the surface. Other species 
make no attempt to burrow, continuing to crawl actively about for two 
hours, at the end of which time the experiments were usually ended. We 
find represented in these species evidently several stages in the development 
of the subterranean habit, some entering the soil very readily, others wee 
apparent reluctance, and some not at all. 


293] NOCTUID LARVAE—RIPLEY 51 


Unavoidable differences in the physiological condition of the individuals 
account, most probably, for the considerable variation in the “‘time required 
for submergence” with different larvae in the same experiment. During 
the rest period prior to ecdysis and some six hours before it, larvae make no 
attempt to burrow when subjected to the test, no matter how pronounced 
this habit may be in the species. Three individuals of Polia renigera which 
reacted differently from the rest, failing to enter the soil, were isolated and 
found to be parasitized by chalcids when they died several days later. One 
larva of Agrotis c-nigrum, presenting a similar non-conformity to specific 
habit, died of the fungus, Botrytis rileyi, some time afterward. This 
individual revealed a marked negative geotropism, crawling up on the sides 
of the jar and onto the thermometer, a reaction exhibited by no other larva 
investigated. It is interesting to note in this connection that grass- 
hoppers diseased by Empusa gryllidae and army-worms or cut-worms 
affected by wilt present the same response, crawling always to the top of 
some plant to die. Underfed larvae require a much longer time to bury 
themselves than do well-fed ones of the same species, the hunger stimulus 
seeming to partially overcome the negative response to light. Experiment 
3 illustrates this point very clearly, the material having been kept without 
food for twenty-four hours in the warm laboratory at a temperature at 
which the metabolism is high. Since the larvae were very hungry, they 
resisted the tendency to burrow for a much longer time than in the other 
experiments, where they were well-fed. For this reason the averages given 
in this table do not include Experiment 3. The difference in the time of day 
when these experiments were performed bears a direct relation to the 
hunger, since the larvae feed principally at night. In Experiment 1, per- 
formed at 9 P.m., the slower response may be due to the fact that feeding was 
interrupted. The difference in weather conditions prior to the performance 
of Experiments 1, 2, and 4, undoubtedly has contributed further to the lack 
of physiological uniformity in the material used, introducing an additional 
source of error. 

Altho accurate data as to the relative facility with which various species 
enter the soil can be obtained only by a long series of experiments carried on 
under carefully controlled conditions, employing a much larger number of 
individuals than have been available for use in our investigation, the data 
presented afford, nevertheless, some significant indications. Since species 
such as the arboreal Homoptera lunata or the cabbage looper, Phytometra 
brassicae, which we know to be not subterranean, are not induced to enter 
the soil under the conditions of the experiments and since notoriously 
subterranean species readily manifest their ability to burrow when stimu- 
lated by light, we are justified in applying this test in order to determine 
whether larvae have subterranean tendencies in species with which this 
point is doubtful. It has been determined thus that the bronzed cut-worm, 


$2 ILLINOIS BIOLOGICAL MONOGRAPHS [294 


Nephelodes emmedonia, and the cut-worms of the genus Cirphis (the army- 
worm genus) are not subterranean. Furthermore, in the subterranean 
species the relative facility with which the larvae enter the soil, as indicated 
by the ‘“‘time required for submergence,” as well as by various peculiarities 
already discussed associated with burrowing, serves as an indication of the 
extent of the development of the subterranean mode of life in these species. 
It may be noted, for example, that Sidemia devastatrix presents an extreme 
case of development of the under-ground mode of life in noctuid larvae. 
The larva of this species rarely comes above the surface except to molt. 
Unlike other cutworms it has lost its body pigment and has been aptly 
described as “half way between a cut-worm and a white grub.”? Owing to 
the insufficiency of material and to the sources of error previously men- 
tioned, it would seem unwise, however, to attach undue significance to the 
relative lengths of time required for burying given in this table. 


RESISTANCE TO SUBMERGENCE 


The object of the second series of experiments is to determine the 
relative resistance to submergence in water in various species of noctuid 
larvae. Immediately after an unusually heavy thunder-shower, several 
arboreal noctuid larvae were found dead, clinging to the trunks of trees in 
crevices in the bark, where water had been running during the hardest part 
of the rain, which had lasted about twenty minutes. Since lightning had 
not struck in the vicinity, it seemed evident that these larvae were drowned 
by the water running down the tree-trunks. They bore the characteristic 
marks, to be described later, of drowned larvae. A few days afterward a 
cut-worm, Feltia subgothica, accidentally left in water for two days in the 
laboratory, recovered after a number of hours and resumed feeding. This 
striking difference in the ability to resist submergence in water between the 
arboreal caterpillars and the subterranean Feltia suggested the use of the 
length of time during which larvae could resist such submergence as an 
index as to the extent of the development of their subterranean habit. 
During early spring land infested with cut-worms, many of which hiber- 
nate as partly grown larvae, is often saturated with water for days at a 
time, without seemingly affecting their numbers. We should naturally 
expect such insects to be able to withstand these conditions successfully and 
to have developed, in common with subterranean animals generally, a 
resistance to submergence. Non-subterranean larvae of the ground- and 
field-strata might be expected to possess this power to a lesser extent, and 
arboreal species would presumably lack it almost entirely, since the nature 
of their habitat usually renders it unnecessary for them to withstand 
extensive drenching. Caterpillars which hibernate in the soil must be sub- 
jected to water from the melting snows as well as to the spring rains and 
consequently might reasonably be expected to present the most extensive 
resistance to submergence of any lepidopterous larvae. 


295] NOCTUID LARVAE—RIPLEY 53 


This subject has been investigated experimentally in order to obtain 
so far as possible a means of expressing mathematically the relative 
“subterraneanness” of various species of noctuid larvae. The material 
used in these experiments was reared under approximately natural condi- 
tions. Before being submerged in water the larvae were washed to remove 
all soil and particles of foreign matter such as might carry minute air 
bubbles beaneath the surface. Immediately after washing, each larva was 
put in 150 cc. of distilled water five cm. deep contained in a small glass jar. 
When the larvae were small, two or three were usually put together in the 
same jar. In order to keep conditions as constant as possible throughout 
this series of experiments, the jars were kept in a constant temperature 
chamber at about 17 degrees C., there being occasionally a deviation of one 
or two degrees in either direction for a few hours at a time. They were 
exposed to natural light but not to direct sunlight. At the end of the period 
of submergence the larvae were dried on filter paper, then placed on a 
blotter six inches below a fifty watt Mazda electric light. Subjected to 
the stimulation of this irritating factor, manifestations of life could be most 
readily brought forth. While in this situation, the time required for the 
individuals to regain various degrees of activity was recorded. They were 
kept under the light for lengths of time varying from fifteen minutes to 
three hours or more, depending upon the readiness with which activity was 
regained. When stimulated as much as possible by this means, the 
individuals were isolated, each being placed under approximately natural 
conditions with food, in order that observations on the later effects of sub- 
mergence might be made for several days. 

The first few seconds of submergence are always spent in violent move- 
ments of the entire body, after which the larva suddenly becomes motion- 
less, remaining so until removed from the water. Individuals undergoing 
ecdysis float, necessitating their being weighted down by a small piece of 
metal tied to the anal uropods by a fine thread. It seems probable that 
there may be a layer of air between the old and new cuticle, which would 
account for the low specific gravity of larvae in this condition. When not 
molting, they always sink immediately. After being removed from the 
water, dried, and placed under the light, the first signs of life are usually 
represented by the beating of the heart, which can be observed according 
to the transparency of the integument. Slight movements of the antennae 
and thoracic legs are next to be seen, followed by a feeble curling of the 
thorax caused by contractions of the longitudinal muscles, often accom- 
panied by an extension and retraction of the crochets. As various kinds 
of motion of the trunk and appendages become more marked, water is 
expelled in quantity from the mouth and anus. When in this stage of 
recovery, larvae placed with the ventral surface uppermost gradually turn 
over. Sometime later they will crawl a little when mechanically stimu- 


54 ILLINOIS BIOLOGICAL MONOGRAPHS [296 


lated, still expelling water. Often after a few hours they appear normally 
active, altho seldom feeding until several hours after apparent recovery. 
The evidences of the regaining of activity take place almost invariably 
in the above order. 

The stage of activity reached with individuals which fail to recover 
varies according to the resistance of the species and to the length of time 
submerged. When kept under water for a time much longer than that 
required for drowning, sometimes no movement can be produced by 
stimulation. More often, however, the earlier stages of activity are passed 
through, followed by a decline evidenced by a repetition of the same stages 
in reverse order. Frequently larvae which have apparently thoroly 
recovered, crawling actively about, refuse to eat and die within two or 
three days. This indicates that the length of time for which they were 
submerged is very close to the minimum time required for drowning for the 
species in question. 

The extent of activity developed before the decline sets in offers a 
valuable guide to the determination of the minimum time required for 
drowning, which is the object sought in these experiments, since this factor 
enables us to express in numbers the resistance to submergence of various 
species. From the data collected it has been possible in most cases to 
determine within rather narrow limits the average minimum time required 
for drowning. When one-half or one-third of the individuals of an experi- 
ment die and the rest survive, the time for which they were submerged is 
taken as representing approximately the resistance to submergence for the 
species. 

Altho different instars of the same species present no uniform difference 
in resistance, we find some individual variation in this respect, which is 
most probably to be accounted for by unavoidable physiological differences 
in the material. Such factors as the time expired since molting, the amount 
of food in the alimentary canal, and the weather conditions under which the 
material was reared undoubtedly influence the resistance to submergence 
to a greater or less extent. The first of these, which will be discussed later, 
is probably the most important. It is to be regretted that data regarding 
the resistance of larvae of different broods have not been obtained, since 
such data would be of considerable interest with respect to those species 
having several broods a year and hibernating as partly grown larvae. Our 
experiments with such species have been performed solely with larvae of 
the hibernating brood after hibernation had been passed. Very probably 
those of the summer broods are less resistant. If this be true, it would be of 
great interest to determine whether the difference in resistance in different 
broods is innate or induced by climatic factors. 

The specific variation in resistance to submergence is extreme, ranging 
from 25 minutes to 48 hours. The exact nature of the adaptations, mor- 


297] NOCTUID LARVAE—RIPLEY 55 


phological or physiological, which permit of such striking differences in this 
respect, is problematical. We find no external structures which throw light 
on this question. The spiracles offer no variations which seem to bear on 
this point. Internal structures or histology, a study of which the scope 
of this work does not permit, may be found to bear relation to the develop- 
ment of the power to withstand submergence. It seems probable that 
differences in the efficiency of the mechanism for closing the tracheae just 
entad of the spiracles may be found. 

There are indications that death from drowning in these larvae is 
caused by two factors, oxygen starvation and mechanical injury due to the 
filling of the alimentary canal with water. The drowned larvae have 
always exhibited a black girdle around the body, varying in extent from 
one segment to five or six, so that in the latter case it extends for half the 
length of the larva. Those which almost recover from submergence show 
but a slight ring around the metathorax or first one or two adbominal 
segments, while individuals which die before their removal from the water 
often turn black from the head to about the sixth abdominal segment. 
Larvae killed by pinching have exactly the same appearance. This appears 
to indicate mechanical injury caused by distending the alimentary canal 
with water. The expulsion of water from both mouth and anus during 
recovery has already been mentioned. It is a significant fact that larvae in 
the prepupal condition and those undergoing ecdysis are much more resis- 
tant than others. Of these the prepupae swallow water and the moulting 
larvae do not, owing to the fact that the mouth-parts cannot function 
during ecdysis; yet the former show at least as great a resistance as the 
latter. Larvae passing through these two stages are physiologically 
similar in the following respects: they are quiescent; they are not digesting 
food, having expelled the contents of the alimentary canal; and they are 
preparing to shed their cuticle. We have reason to suppose that the oxygen 
requirement for both prepupae and molting is relatively low, due to the 
reduction of motion and to the lack of digestion of food. In the light of this 
probability the great resistance to submergence of larvae in both of these 
stages becomes understood. Death by drowning seems to be effected, then, 
both by lack of oxygen and by mechanical injury due to gorging the digestive 
tube with water. How subterranean larvae are equipped to withstand 
either or both of these factors, we do not know. 

The resistance to submergence in different species, as determined 
experimentally, varies according to the extent to which the larvae are 
subjected to submergence or to drenching in their natural habitats. This 
resistance is not only correlated with the proximity of the habitat to the 
ground during the active life of the larva, but also with the stage in which 
the hibernation is passed, since larvae passing the winter in the soil must 
withstand considerable submergence without regard to their habitat while 


56 ILLINOIS BIOLOGICAL MONOGRAPHS [298 


in an active condition. In order to present more clearly the relations shown 
in the data collected, it has been divided into two sections, the first of which 
includes only, those species hibernating as larvae on or beneath the ground, 
the second section embracing those not passing the winter in this stage. 
If we compare two equally subterranean species, one of which hibernates in 
the soil as a larvae, the other as a pupa, we note that the former is very 
much more resistant to water. Feltia subgothica and Agrotis ypsilon or 
Nephelodes emmedonia and Phytometra brassicae afiord examples of this 
point. It is evident, then, that we should confine our comparisons of the 
resistance to submergence of species, with reference to their habitats, to 
those which fall in the same section. By so doing the factor of the stage 
of hibernation is eliminated. 

It has been found that the subterranean species present the greatest 
resistance. Epizeuxis lubricalis, because of its exceptional mode of life, 
cannot properly be compared to other species in this section. Altho never 
entering the soil, it remains in wet weather in or beneath water-soaked 
pieces of decaying wood on the ground, dead-wood furnishing the food for 
this biologically specialized species. Consequently, it presents a high 
resistance, altho non-subterranean. ‘The relative development of the 
power to resist water in species of the subterranean-, field-, and tree-strata 
is indicated in Section 2, in spite of the insufficiency of the data. Most 
resistant is the fairly subterranean Lycophotia margaritosa, next the non- 
subterranean cabbage looper, Phytometra brassicae, of the field-stratum, 
and least so the arboreal forest-species, Homoptera lunata. 


EPICRANIAL INDEX AND SUBTERRANEAN HABIT 


This investigation of the resistance to submergence in water leads us to 
conclude that this factor is an index to the extent of the development of the 
subterranean mode of life, altho hibernating larvae cannot be directly 
compared in this respect with those not passing the winter in this stage. 
We have now established two criteria for determining the relative ‘‘sub- 
terraneanness” of species, namely, the readiness with which the larvae 
enter the soil and their resistance to water. The latter, since it is capable of 
numerical expression much more accurately than the former, is far more 
significant as a guide to the extent of the development of this habit. 

It has been stated previously that the epicranial index is correlated 
with the subterranean habit, those species presenting the most marked 
underground mode of life having the shortest epicranial stem. Having 
necessarily disgressed from our principal line of thought, in order to 
establish the relative ‘“‘subterraneanness”’ of various species, we are now 
prepared to continue our consideration of this suture. We have already 
shown that the short epicranial stem or large epicranial index isan excep- 
tional condition in lepidopterous larvae, associated with a specialized feed- 


299] NOCTUID LARVAE—RIPLEY 57 


ing habit. The data confirms not only that this condition in the Noctuidae 
is confined to subterranean larvae, but that the extent of the development 
of this habit is correlated very definitely with the relative length of the 
epicranial stem. We have ample reason, therefore, for stating that the 
short epicranial stem is a specialized condition in noctuid larvae, associated 
with a specialized mode of life, the subterranean one. 

Our understanding of the mechanics of this correlation is by no means 
complete. Subterranean larvae are characterized in general by an extensive 
chitinization of the pronotum, beneath which the caudal part of the head is 
retracted most of the time. The mouth-parts tend to become directed 
cephalad instead of ventrad in such larvae. A parallel, but more extreme 
condition is exhibited by the lepidopterous leaf-miners, where we find the 
greatest reduction of the epicranial stem correlated with mouth-parts 
directed cephalad, the caudal portion of the head remaining beneath the 
chitinized pronotum. It seems evident that mandibles in this position are 
better adapted for burrowing than those directed ventrad, and that this 
change in the position of the head has induced a shortening of the epicranial 
suture, a point which has been discussed in the morphological section of this 
paper. When we consider the profound specialization in the heads of 
beetles, which has been brought about in correlation with the change in the 
position of the mouth-parts from a ventral to a cephalic direction, it seems 
quite reasonable to suppose that a less marked specialization in the position 
of the head, such as we find in subterranean noctuid larvae, would be 
accompanied by proportionately less pronounced modifications of the 
head-capsule. 

Our knowledge of this relation between the epicranial stem and the 
feeding habit should be of some value to the economic entomologist. 
Cut-worms attacking well-cultivated crops, such as corn or tobacco, must 
be able to enter the soil in order to protect themselves from the heat of the 
sun. The larvae of those species which do not burrow must depend upon 
an abundance of grass or weeds, among the bases of which they can with- 
draw during the brighter part of the day. Noctuid larvae with a long 
epicranial stem, such as the bronzed cutworm, Nephelodes emmedonia, or 
the members of the genus Cirphis, to which the army-worm belongs, are 
unable to enter the soil and are therefore seldom found attacking well 
cultivated crops. When such crops are attacked by army-worms, it is 
during migratory outbreaks, when their reactions are abnorma:. It isa 
significant fact that all of the fourteen species dealt with by Crumb in his 
key to tobacco cutworms are of the short-stemmed type. The army-worm’s 
abstinence from tobacco is not a matter of appetite, since this author has 
found them to eat it as readily as grass, but it is rather because of the 
inability of this species to burrow into the earth and thus escape the rays 
of the sun. Hence an examination of the length of the epicranial stem of an 


58 ILLINOIS BIOLOGICAL MONOGRAPHS [300 


undetermined cutworm may inform the field-man whether or not it could 
consistently attack any well cultivated crop. 

The changes in the epicranial index, length of front divided by length 
of epicranial stem, undergone in the postembryology of various species are 
presented in the tables. The percentage of variation has been computed in 
the same way as in Table I. The measurements were made with an ocular 
micrometer. It wi!l be noted that the greatest individual variation occurs 
in the last instars of the most subterranean species, which present the most 
specialized condition of the epicranial stem. The postembryonic develop- 
ment of the epicranial index has been graphically expressed in Plate I. 
The horizontal axis has been divided into six equal parts representing 
stadia, this being the usual number within the family. With those species 
presenting five or seven stadia, the units on the horizontal axis have been 
respectively lengthened or shortened so that the total length of this axis 
remains the same for all curves. By this means curves of species having a 
different number of instars can be more easily compared. The interpreta- 
tion of this chart presents some very significant points, which we shall con- 
sider singly. These curves may be conveniently divided into two types. 
The curve of the first type turns upward toward the right and shows a 
marked shortening of the epicranial stem in the later stadia, while that of 
the second type continues downward and reveals a continuous lengthening 
of this suture. The significance of this turning upward, presented by the 
first type, will be considered at this point. 

It has been well established in our discussion of the phylogeny of this 
structure that in this family the short epicranial stem has descended from 
the longer more primitive one. Since the curves of those species whose last 
instars present a reduced condition of this suture reveal the presence of a 
longer one in one or more of the preceding stadia, we must conclude that 
the postembryology of this structure recapitulates its phylogeny. In our 
classification of the kinds of postembryonic changes, those involving the 
relative length of the epicranial stem fall, therefore, under the recapitulative 
type. 

The curves of all species of Noctuidae examined reveal a lengthening 
in the stem from earlier to later stadia or to the stage in which the turning 
upward takes place. In the three species examined representing the 
families Notodontidae, Liparidae, and Psychidae, we find this same condi- 
tion, altho not very marked in the first of these, indicating apparently that 
this suture was short in the ancestral larva of these families, and possibly in 
all the Lepidoptera. We have, however, no phylogenetic evidence in 
support of this indication, since the larvae of the most generalized families 
usually have specialized feeding habits, rendering it unsafe to regard a - 
structure whose condition is correlated with the feeding habit,as we have 
shown that of the epicranial stem to be, as representing a generalized con- 


Y 


301) NOCTUID LARVAE—RIPLEY 59 


dition in these larvae. This suture is fairly long in the root-boring larvae 
of the three species of Hepialus examined. In the larva of the European 
cossid, Cossus cossus, we find an unusually short epicranial stem, while 
Zeuzera pyrina shows the opposite extreme, altho both are borers in live- 
wood. The bag-worm, Thyridopteryx ephemeraeformis, offers an average 
condition of the epicranial index. It is probable that none of these species 
presents a generalized condition with respect to this structure, altho they 
represent generalized families. Since the turning upward toward the right 
of the chart, wherever it is found in these curves, evidently expresses a 
recapitulation of the phylogeny of this structure, it seems reasonable to 
conclude that the turning downward toward the left in the same curves 
represents also a recapitulation. The lack of change in epicranial index 
from first to second instars in the two species of Phytometra examined, as 
well as the turning upward shown by the curves of various other species, 
precludes all possibility of explaining this lengthening of the epicranial stem 
in terms of the mechanics of growth. There is no mechanical force, in 
other words, producing more rapid growth in the vertex than in the front. 
Hence, in the absence of knowledge concerning the early phylogeny of this 
suture, such data as we have indicate that the ancestral noctuid larva 
possessed a short epicranial stem, altho this condition is found in existing 
forms only as a secondary development associated with the subterranean 
mode of life. 

We will consider now the interpretation of the fact that the change in 
direction in those curves which turn upward takes place in different stadia 
in different species. This interpretation involves, in the first place, an 
analysis of the postembryological relation which corresponding stadia in 
different species bear to one another. Do corresponding instars in species 
having the same number of stadia necessarily represent identical post- 
embryological stages? Various mammals at the time of their birth present 
somewhat different developmental stages. The kangaroo, for instance, 
brings forth its young in a very immature condition, corresponding to 
that found in the late embryonic life of the majority of mammals. It seems 
not unlikely that insects may offer a parallel situation, the early postem- 
bryonic life of some corresponding, perhaps, to the latter embryonic life of 
others. Within a group as closely related as the noctuids it seems very 
improbable that such a condition should exist to any appreciable extent, 
altho we cannot be sure that all noctuid larvae are equally mature at 
hatching. However, this may be, it is certain that the passing of cor- 
responding stadia requires quite different proportional lengths of time in 
different lepidopterous larvae, even within the same family, suggesting the 
possibility that the postembryological value of such stadia may differ 
according to the species. If we find, for example, the first stadium of one 
species requiring one-third of the total larval life and that of another species 


60 ILLINOIS BIOLOGICAL MONOGRAPHS [302 


but one-eighth, we naturally begin to doubt that this stadium represents 
the same stages of development in these species. The data presented will 
serve to illustrate this condition. We note that the time required to pass 
various stadia relative to the total larval life varies considerably in species 
and to some extent in individuals. The question arises as to how much of 
this difference is due to external factors and what proportion of it is attrib- 
utable to innate tendencies. The effects of change of temperature, of 
starvation, and of parasitism upon individuals of Polia renigera are very 
marked, as is the influence of seasonal conditions upon different broods of 
Coramica picta, demonstrating the pronounced effect of external factors 
upon the length of stadia. The innate tendencies in this respect can be 
determined accurately for various species only by rearing their larvae under 
constant conditions, as has been done with Polia renigera and A grotis 
ypsilon. These were reared at both 28 degrees C. and 21 degrees C. in 
ventilated jars at 100% relative humidity. The individual variation in the 
relative length of the stadia of the few individuals which were so reared we 
cannot satisfactorily explain. Larvae of these two species reared outside do 
not differ uniformly in the proportional length of their stadia from those 
grown under constant conditions. 

The lack of data derived from rearing larvae in this manner precludes 
our drawing definite conclusions as to the innate relations existing between 
the duration of different stadia in different species. Nevertheless a com- 
parison of species reared outside may offer us significant indications regard- 
ing this point. It will be noted that the larvae of two species of tussock- 
moths, Notolopha antiqua and Hemerocampa leucostigma, which were reared 
by Payne in Nova Scotia under natural conditions, present a relatively 
long first stadium. Larvae hatching from forced hibernating eggs of the 
latter species in Illinois and grown in a warm laboratory by the author 
also required an unusually long period for passing this stadium, indicating 
that this unusual condition is not to be explained by the effect of external 
conditions upon the larvae. Nor is it correlated with hibernation in the 
egg stage, since three species of larvae of Catocala hatching from hiber- 
nating eggs about the same time failed to show this condition, the first and 
second stadia requiring about an equal amount of time. In all noctuid 
larvae reared by the author the last stage has been markedly the longest, 
whereas in these two species of liparid larvae the last two stadia are nearly 
equal in duration. The three larvae of Dipterygia scabriuscula, showing the 
long first stadium, hatched on the same day as the fifty-one individuals of 
Agrotis ypsilon and were reared under the same conditions, yet all of the 
latter species required approximately the same amount of time for passing 
first, second, and third stages. In Polia renigera there seems to be a general 
increase in the length of the two latter stadia, while only the last stage is 
long in A grotis ypsilon and Lycophotia margaritosa. These facts all indicate 


303) NOCTUID LARVAE—RIPLEY 61 


the presence of innate differences in the relative length of corresponding 
stadia in different species, even within families. 

The presence of such a difference, however, need not necessarily indi- 
cate a difference in postembryological value of the corresponding stadia of 
the species compared, since the longer stadia may be associated with 
slower development. The fact that the amount of increase in the width of 
the head-capsule from one stage to the next remains practically constant for 
the species, bearing no relation apparently to the duration of the stadia, 
shows that the longer stadium represents the slower growth. For example, 
Dipterygia scabriuscula requires a much longer relative time for passing 
the first stadium than does Lycophotia margaritosa, yet both species grow 
approximately equal amounts during this stage, the former growing more 
slowly than the latter. Since the first instars of these two species grow 
relatively the same amount, it seems quite probable that they present the 
same postembryological stage at the end of the first stadium, nowithstand- 
ing the specific difference in the duration of this stadium. However, this 
is not necessarily true, for it is easily conceivable that corresponding instars 
of two species might grow relatively equal amounts and yet attain different 
stages of development. Much investigation on the postembryology and 
physiology of these larvae must be completed before we shall be able to 
settle definitely this question as to the exact relations which the duration 
of the stadium and the amount of growth bear to the stage of postembryonic 
development. 

It is highly probable, however, that corresponding stadia in closely 
related species represent about the same stages in postembryology. Altho 
the first stadium of one species may possibly correspond embryologically 
to the first and part of the second in another or perhaps the third instar of 
one may represent in development the latter part of the third and first half 
of the fourth in another, it seems practically impossible that the develop- 
mental differences within this family could be sufficiently profound to 
render the first stadium of one species equivalent postembryologically to 
the third of another or the fourth of one to the sixth of another. Whatever 
minor variations in this respect may exist in those species whose curves turn 
upward would certainly not be sufficiently extensive to mislead us in 
interpreting these curves. 

From our conception of the law of recapitulation it follows as a corollary 
that identical stages of development in different species must represent the 
same period in phylogeny with reference to the recapitulation of a particu- 
lar structure. This corollary may be stated thus: Any recapitulative 
change must recapitulate in equivalent stages of development in different 
conditions of species which have developed during the same phylogenetic 
period. It follows, of course, that postembryological stages which are not 
equivalent must present conditions with respect to a particular recapitula- 


62 ILLINOIS BIOLOGICAL MONOGRAPHS [304 


tive change which have developed at different times in race-history, the 
earlier stage in the ontogeny representing the earlier phylogenetic period. 
For example, when we find the epicranial stem, which we have shown to be 
a recapitulative structure, beginning to shorten in the second stadium of 
one species and not until the fifth of another, we conclude that this condi- 
tion developed in the former species in a much earlier phylogenetic period 
than in the latter. 

We cannot be reasonably certain of locating equivalent postembryologi- 
cal stages in different species unless they be rather closely related. In 
attempting to find developmental stages in a lepidopterous and a coleop- 
terous larva, for instance, which we could be certain were identical, we 
should encounter, no doubt, considerable difficulty. The former might be 
more mature at hatching than the latter and they might pupate at some- 
what different postembryonic stages. Furthermore, various structural 
and developmental specializations might render it practically impossible 
to locate exactly corresponding postembryological conditions in the larvae 
of these two orders. Tower has shown that beetle larvae present marked 
developmental diversity within themselves, the wings of certain chrysome- 
lids being distinguishable at the time of hatching from the egg, whereas in 
the Curculionidae, and some other families they do not appear until the last 
larval stadium. By going back sufficiently far into the embryology we 
could undoubtedly locate equivalent stages in the most diverse orders of 
insects, but in the postembryology we must confine the application of this 
corollary to closely related species, where no marked developmental or 
structural diversity threatens to mislead us. . 

We have already concluded that corresponding stadia of those species 
whose curves turn upward may be regarded as representing approximately 
equivalent postembryonic stages. It becomes evident upon the application 
of the corollary just discussed that these stadia also correspond to more or 
less definite periods in phylogeny. Each unit on the horizontal axis of the 
chart represents roughly, then, a definite postembryological stage and an 
equally definite period of time in race-history. The relation which these 
units bear to one another we need not consider at this point. It will be 
shown later that certain biological evidence supports the application oa this 
corollary to our intepretation of these curves. 

Plate I shows conclusively that the short epicranial stem has appeared 
independently in different species during widely separated periods in the 
ancient history of this family, since the shortening of this suture begins as 
early as the second period in some but not until the last in others. Hence 
the short-stemmed species do not constitute a phylogenetic unit, a point 
which will be discussed in detail later. 

The progressive nature of the tendency toward the shortening of the 
epicranial stem is very apparent in these curves which turn upward. In 


305] NOCTUID LARVAE—RIPLEY 63 


but one or two instances among the noctuid larvae examined has the 
relative length of this suture remained unchanged after it has ceased to 
lengthen and never has it grown subsequently longer after once beginning 
to shorten, but it has continued to become progressively more reduced 
with the passing of time. The species which began to exhibit this reduction 
earliest in their race-history generally present the shortest stem in their 
last instars. This does not necessarily hold true in all cases, however, since 
some species had a much longer epicranial stem than others at the time 
when this suture commenced to decrease in length, so that the greatest 
reduction in the last instar is not always correlated with the earliest appear- 
ance of this shortening. A comparison of the curves of Polia renigera and 
meditata will serve to illustrate this point. Moreover, there is a marked 
diversity in the angle at which the curves of different species turn upward, 
so that a form which has been developing in this direction during the last 
period only may have a shorter stem in its last instar than one in which this 
suture has been decreasing for a much longer period. To use a convenient 
analogy, some have run faster than others, some have had farther to go, 
and some began to run much earlier than others, the latter having won the 
race in the majority of cases. 

Certain species, such as Cirphis phragmitidicola, apparently represent 
an incipient stage in this process of reduction, which, if it continues to 
operate progressively in the future, as it has in the past with other species, 
must result eventually in reducing the epicranial stem of this species to a 
fraction of its present length, a condition typified at present by the last 
instars of Agrotis ypsilon and Feltia subgothica. 

To summarize the conclusion which we have thus far reached regarding 
the shortening of the epicranial stem in the postembryology of noctuid 
larvae: This process is a recapitulative one. It represents a secondary 
development occurring only in certain species with subterranean pro- 
clivities. It is of independent origin in different species, having begun at 
widely different times in race history. It is a progressive process, species 
in which it has begun continually undergoing greater reduction in the 
length of this suture. The intensity of this process has varied in different 
species, that is, it has gone on more rapidly in some species than in others. 

In the following discussion, it will be shown that the rate of reduction 
in the length of the epicranial stem has been subject to an acceleration. 
The significance of the slopes and angles of both types of curves will now be 
considered. Certain of them turn upward at a smaller angle than others in 
the same period, indicating unequal rates of reduction in the stems of such 
species, as has been stated previously. A parallel situation may be seen in 
the left-hand portion of the curves, where some turn downward much more 
abruptly than others, showing that this primary lengthening process has 
also developed at very different rates according to the species. It should be 


64 ILLINOIS BIOLOGICAL MONOGRAPHS [306 


clearly borne in mind that these conclusions are based on a comparison of 
angles presented by different curves in the same horizontal unit. Such a 
comparison can be directly interpreted without danger of going astray, 
but in comparing the slopes of parts of the same curve or of portions of 
different curves in different units, we are confronted with a situation which 
is liable to be misleading without an understanding of the relation which 
these units bear to one another. 

For the purpose of analyzing this relation let us suppose that a certain 
species has a larval life of sixty days, which we will divide without regard 
to stadia into six equal periods of ten days each. Suppose further that we 
represent the curve of this species as we have those in Plate I, using for 
units, however, these six equal periods instead of stadia. Now in this 
graphic representation, the periods in phylogeny to which these ten-day 
divisions correspond are given equal value, whereas in reality this is very 
far from true. According to the general conception of the working of the 
law of recapitulation, the first ten days would represent a much longer 
phylogenetic period than the second ten, which, in turn, would correspond 
to a portion of the race-history of much greater duration than would the 
third ten days, and so on until the last ten day division, whose correspond- 
ing phylogenetic period would be, perhaps, but a minute fraction of that of 
the first ten days. The fact that the change in the position of the setae of 
the trunk, a recapitulative one, is very much greater from first to second 
instars, than thruout the entire remainder of the larval life illustrates this 
principle. To represent graphically this condition it would be necessary to 
extend greatly the length of the first unit, lengthening the second one to a 
lesser extent, the third a still lesser amount, and so on. ._ We have no means 
of knowing what the relative lengths of these units should be in order to 
render the slopes of different parts of this hypothetical curve exactly repre- 
sentative of the relative rates at which these changes in epicranial index 
have evolved during different phylogenetic periods. We merely know in 
which direction to apply this sort of correction. 

Another means of correction may be applied to this hypothetical curve, 
by leaving the units equal, as they are in Plate I, but dividing the sixty 
day larval life into six unequal periods, which gradually increase in length 
from younger to older. The same result would be accomplished in this 
manner as by keeping the periods equal and altering the length of the 
units, in the manner just described. For mechanical reasons it has been 
necessary to use stadia for our units in Plate I. As already demonstrated 
the lengths of stadia generally do not present a gradual increase from 
younger to older in this family, but are often about equal, except for the 
last, which is usually much longer, and for the first, which is long in some 
species. The employment of stadia as units, then, offers no correction, 
except possibly for the last unit, where this stadium is long. It is question- 


307} NOCTUID LARVAE—RIPLEY 65 


able whether or not this correction, brought about in consequence of the 
longer duration of the last larval stadium, where this condition is found, 
is sufficiently extensive to render significant a comparison of the slopes 
of the last two units without further correction. Possibly these two units 
may remain equal as they stand in Plate I, the long last stadium having 
taken care of the correction, which would otherwise have to be introduced 
by increasing the length of the next to last unit. Where we find a long first 
stadium we should perhaps increase the length of the first unit even more 
than otherwise. It is well to recall at this point, however, that the length 
of a stadium may not be an index to the amount of postembryonic develop- 
ment undergone during it, since, as has been previously suggested, the 
longer stadium may be correlated with a slower development. If this be 
true the long first stadium requires no greater correction than the shorter 
one. 

When we compare different parts of the same curve, then, with refer- 
ence to slope, it must be remembered that the units should not be of equal 
length, as they stand in Plate I, but that each should be somewhat longer 
than the one which follows it. The possibility that the last two units may 
need little or no alteration in order to represent the true condition should 
also be considered. Furthermore, the first unit may require greater length- 
ening than otherwise for species with a long first stadium, such as Dip- 
terygia scabriuscula. The general effect of this correction is to make the 
primary curving downward on the left of the chart very gradual and to 
accentuate the secondary curving upward on the right. Upon applying 
this correction mentally to Plate I, we note that this secondary shortening 
of the epicranial stem has proceeded with much greater rapidity than its 
primary lengthening. It becomes evident, moreover, that this primary 
process has generally accelerated with the passing of time, altho the curves 
seem to indicate the opposite condition before the necessary correction is 
applied. Straight lines, where they occur on the uncorrected chart, do not 
indicate a constant rate of evolution, but an acceleration. The secondary 
shortening process has also progressed at an increasing rate, the accelera- 
tion being much greater than in the lengthening process. 

The two species of the genus Phytometra examined present a distinct 
type of curve in which the epicranial index remains unchanged thruout 
the first two periods, followed by the usual accelerated lengthening. The 
epicranial stem of the last instar of these larvae is as short as that of the 
average species whose curve turns upward. This condition is evidently due 
to the fact that in this genus the primary lengthening has been delayed 
until the third period, so that the epicranial stem has not been evolving in 
this direction for a sufficiently long time to enable it to attain the length 
common to species in which this suture has not undergone secondary 
reduction. 


66 ILLINOIS BIOLOGICAL MONOGRAPHS [308 


This postembryological study has provided a source of evidence as to 
the evolution of habit within this family. The correlation between the 
reduced condition of the epicranial stem and the subterranean mode of 
life has already been discussed. We have seen that an anatomical relation 
exists between the short epicranial stem and the cephalic direction of the 
mandibles, this latter condition beg apparently an adaptation for bur- 
rowing in the soil. The period in phylogeny in which the shortening of this 
suture began, as indicated by the curves in Plate I, is to be regarded, then, 
as the one in which this biological specialization took place. The point of 
turning upward in one of these curves represents, in other words, the origin 
of the subterranean habit in the race history of the species in question. It 
is apparent that this mode of life has originated independently at different 
times in the phylogeny of different species. Entomology furnishes numer- 
ous instances of such independent origin of the same biological specializa- 
tion in various groups of insects. The aquatic and parasitic modes of life, 
as well as the leaf-mining and wood-boring habits exemplify this situation, 
the same habit having developed independently at different times in 
different groups. 

We have demonstrated the accelerative nature of the secondary shorten- 
ing of the epicranial stem. In the light of the established correlation be- 
tween this structure and the subterranean habit, it becomes evident that 
species developing tendencies to enter the soil have gradually become more 
markedly subterranean at an increasing rate with the passing of time. 
From this it follows that those forms having developed this habit earliest 
in race-history must present the most pronounced subterranean mode of 
life at present. From the data we have collected it is clear that this is pre- 
cisely the case. The species whose curves turn upward earliest in postem- 
bryology reveal the greatest degree of “‘subterraneanness,” as evidenced 
by their resistance to submergence and other biological traits. Those 
forms which have been subterranean longest, in other words, are the most 
subterranean now. ‘This point supports further the corollary that cor- 
responding postembryological stages in different species represent the same 
phylogenetic period, inasmuch as the conclusions obtained on the basis of 
this corollary agree with the biological data regarding the relative ‘“‘sub- 
terraneanness”’ of species. 

It has been noted that certain species, typified by Cirphis phragmitidi- 
cola and Ceramica picta, appear to represent an incipient stage in the 
development of the subterranean mode of life, entering the soil only under 
extreme stress during the feeding period. The curves of such forms turn 
upward but slightly, in the last unit only. If the development of this habit 
continues progressively in the future as it evidently has in the past, such 
slightly subterranean species must eventually become markedly so, like 
A grotis ypsilon or Feltia subgothica. This suggests the interesting possibility 


309] NOCTUID LARVAE—RIPLEY 67 


that we may have in the remote future a larger number of species of sub- 
terranean noctuid larvae than at present. However speculative this propo- 
sition may seem, it is undoubtedly indicated by the data at hand. 

When we compare subterranean and non-subterranean larvae with 
reference to the number of individuals parasitized, the advantage of the 
former mode of life becomes obvious. From more than a thousand indi- 
viduals of Feltia subgothica reared during three successive years, but four or 
five have been infested with insect-parasites, whereas larvae remaining 
above ground during the daytime, such as the cabbage-looper or the army- 
worm, are frequently 90% parasitized by many insect-enemies. Subter- 
ranean cutworms are similarly free from attack by birds. Egg-parasites 
affect both classes equally. Fungi and wilt diseases seem to be as generally 
found in non-subterranean hosts as in those whose habitats are associated 
with the earth. The only nematodes thus far recorded from noctuid larvae 
were taken from a single subterranean cutworm, Agrotis sp., by the author. 
The apparent rarity of these parasites in cutworms indicates that they are 
not to be regarded as important enemies. Large carabid beetles are 
evidently the only important natural enemies affecting subterranean 
lepidopterous larvae to an appreciably greater extent than those which 
do not enter the soil. Yet these feed extensively upon larvae above ground, 
some even climbing trees in search of their prey. From the point of view of 
protection from natural enemies, the subterranean habit unquestionably 
offers important advantages, which probably accounts to a large extent for 
its progressive nature in the course of evolution. 

The interpretation of certain exceptional curves in Plate I is proble- 
matical. That of Agrotis clandestina fails to turn upward, altho the larva 
of this species is to some extent subterranean. The primary lengthening 
of the epicranial stem of this species is but slight in the last period, indi- 
cating the retarding of this process, which must necessarily precede the 
secondary shortening. Not only does the curve thus indicate an incipient 
condition in the reduction of this suture, but the bright coloration of this 
cutworm points further to recent development of the subterranean habit. 
Cutworms which enter the soil generally tend either to lose their pigment, 
like Sidemia devastatrix, or to become indistinctly marked and dully 
colored. We know of few equally subterranean larvae with such bright 
colors and distinct markings as clandestina. <A grotis c-nigrum, to which this 
species is very closely related, exhibits similar but much less distinct 
markings and duller colors, its curve being typical of cutworms which 
burrow in the ground. Clandestina is probably one of our “youngest” 
cutworms, this habit, altho quite well developed, being too young phylo- 
genetically to be accompanied by a marked shortening of the epicranial 
stem. 


68 ILLINOIS BIOLOGICAL MONOGRAPHS [310 


Catocala ? vidua presents the opposite situation, where we have an 
arboreal form whose curve turns upward slightly in the last unit. Possibly 
the larva of this species enters the soil to pupate, altho the members of this 
genus typically spin cocoons above the ground. The epicranial stem of the 
arboreal Heterocampa bilineata (Notodontidae) undergoes a marked 
secondary shortening, showing that this condition in families other than the 
Noctuidae is not necessarily associated with the subterranean mode of life. 
In spite of the marked turning upward in the curve for this species, the stem 
of the last instar is much longer than in larvae which enter the soil. The 
peculiar curve of the bag-worm bears some relation, perhaps, to its unusual 
feeding habit. A much more extensive postembryological study of this 
structure must be made, embracing many families of lepidopterous larvae, 
before we can hope to understand the significance of these changes. 

Having discussed the postembryology of the epicranial stem and its 
biological significance, it now remains for us to consider the phylogenetic 
evidence which this study may afford. A certain degree of correlation 
between the types of curves in Plate I and taxonomic groups can be 
observed. Attention has already been directed to the peculiar type of 
curve presented solely by the two representatives of the Phytometrinae 
examined. Whether or not this type is characteristic for the entire sub- 
family we cannot state. When we consider the pronounced uniformity of 
the larvae of this group, however, it seems fairly probable that this is so. 
The species of Catocala represented exhibit an unusually great increase 
in the length of the epicranial stem during the first two periods. Species 
of the same genera have curves similar in position and shape, except where 
the secondary turning upward has interfered. This process, being asso- 
ciated with the subterranean habit, which often differs in closely related 
species, cannot be relied upon as an indication of phylogenetic relationship. 
With curves which turn upward the primary portions only can be safely 
compared from a taxonomic point of view. For instance, Cirphis unipuncta 
presents a typical non-subterranean type of curve, whereas those of 
phragmitidicola and pseudargyria, which are very closely related to this 
species, are of the incipient subterranean type. The difference in the later 
postembryonic development of this suture in Agrotis c-nigrum and clan- 
destina has already been referred to. A comprehensive series of such 
curves would unquestionably afford valuable phylogenetic information. 

All of the species examined were established earlier than the first 
phylogenetic period represented in Plate I. In other words, none of the 
curves of closely related species have started from the same point in the first 
unit. A more extensive series might very possibly discover species so 
recent that their curves would unite in a common line in the first one or two 
units. 


311] NOCTUID LARVAE—RIPLEY 69 


The race-history of the reduced epicranial stem may be represented by 
the diagram shown in figure 61, which indicates both the independent origin 
and progressive nature of this condition. In this figure 1 represents the 
persistence of the long-stemmed ancestral condition to the present. A 
form which has departed relatively recently from the condition of 1 and 
which tends toward the development of a shorter stem is illustrated by 2. 
The most ancient departure from 1 is represented by 6, which reveals the 
shortest epicranial stem at present. The conspicuousness and apparently 
fundamental nature of this character would tempt taxonomists to employ 
it for the division of larger groups within this family. Our knowledge of its 
phylogeny, however, derived from this postembryological study limits its 
taxonomic use to the separating of species and in some cases, perhaps, of 
genera. The taxonomist studying this structure without regard to postem- 
bryological evidence, but drawing his conclusions entirely from the com- 
parative morphology of the last instar, would, in all probability, be misled 
as to its phylogeny. He would, of course, without the aid of postem- 
bryology correctly conclude that the short stem represented a specialized 
condition but, on the other hand, no clue as to the independent origin of the 
shortening of this suture would be afforded him. Working on this basis” 
he would most naturally be led to believe that the species with the short 
epicranial stem represented, at least for the most part, a phylogenetic unit- 
The fact that this condition is often found in closely related genera would 
add to this impression. Its independent origin in different species in the 
same subfamily or genus could not possibly be deduced without a post- 
embryological study. Figure 60 represents diagrammatically the erron- 
eous interpretation of the evolution of the short epicranial stem, which 
would be most naturally derived from a study confined to full-grown larvae. 
In this diagram 1 represents the persistence of the primitive long-stemmed 
condition, as in Figure 61. The short-stemmed condition, on the other 
hand, is shown as descending from a common ancestor. The preservation 
of the condition of the most ancient departure from 1 is illustrated by 2, 
whereas in reality the condition of 2 is the most recent departure in this 
direction. According to Figure 60, 6 has developed most recently and 
reveals the most extreme specialization. In reality the condition of 6 at the 
present time is found in species in which this tendency appeared earliest in 
phylogeny, as shown by Figure 61. A comparison of these two diagrams, 
the correct and the false, derived respectively with and without regard to 
postembryology, demonstrates in a convincing manner the phylogenetic 
value of this neglected source of evidence. 


POSTEMBRYOLOGY OF LABIUM AND SPINNERET 


The most profound postembryonic changes undergone by noctuid 
larvae are those in the form of the spinneret, while other parts of the labium 


70 ILLINOIS BIOLOGICAL MONOGRAPHS [312 


also present considerable difference according to the instar. The stipular 
setae frequently increase in relative size during larval life (Figs. 40, 43, 44), 
altho they may remain about the same (Figs. 33, 38). A striking decrease 
in relative size is always undergone by the two sensoria of the palpiger and 
by the pair of smaller ones on the proximal semicircular sclerite of the 
spinneret (Figs. 29-32, 33-36, 38, 40, 41, 43-45). As previously mentioned 
the same situation is presented by those of the head, altho not so marked. 
This appears to be a non-recapitulative change due to the mechanics of 
growth. The pronounced decrease in the relative size of the ocellarae 
already discussed offers an apparently parallel situation. It seems evident 
that the modified hypodermis of sensory organs, whether of visual or of 
chemical sense, grows more slowly than the ordinary hypodermis. 

In the first instar of some species the proximal sclerite of the spinneret 
is continuous between the sensoria, forming a complete ring instead of a 
semicircle, as it sometimes does in the older noctuid larvae (Figs. 33-38). 
The fact that the former condition is of quite frequent occurrence thruout 
the order suggests that it may be the primitive one, in which case this 
change is to be regarded as a recapitulation, the semicircular scierite of the 
noctuid larva representing the remnant of a complete ring. The first instars 
of Polia renigera and of Agrotis ypsilon, on the other hand, exhibit the 
condition typical of fully grown noctuid larvae with respect to this point 
(Figs. 29-40). In the former species, however, a secondary chitinization 
appears in the last instar, connecting the two ends of the semicircle (Figs. 
31-32). 

The palpi undergo changes in form and in the shape and relative size 
of their setae. A comparison of Figures 30 and 31, 33 and 38, and 40 and 
44 reveals the fact that both segments of the palpus become relatively 
longer and narrower during development. Since there appears to be no 
evidence indicating whether or not the ancestral palpus was shorter and 
broader than the typical one of existing forms, we cannot attempt to 
classify this change. The significance of the striking reduction of the seta 
of the proximal segment during larval growth is also problematical. 
Usually, altho not always, the terminal seta of the distal segment becomes 
much more slender and relatively shorter in the later stadia. Lycophotia 
margaritosa appears to present an exceptional] situation in the development 
of all of the setae of this region. Those of the stipula fail to increase in 
relative size as they usually do and the terminal one of the palpus becomes 
relatively larger in the course of growth, whereas the reverse is typically 
true. The reduction of the terminal seta commonly found in the Noctuidae 
is paralleled in certain leaf-miners figured by Tragardh. Moreover, the 
terminal setae of the antennae and maxillae of caterpillars are frequently 
short and stout in the first instar, becoming normal in form during develop- 
ment. Thesignificance of these changes cannot be definitely determined in 


313] NOCTUID LARVAE—RIPLEY 71 


the present state of our knowledge of their phylogeny. They are probably 
non-recapitulative but are evidently not to be explained by the mechanics 
of growth, since exceptional instances occur. 

It was mentioned in the morphological part of this paper that the seta 
of the proximal segment of the palpus presents a specialized condition with 
reference to position in Lycophotia margaritosa, where it is located mesad 
instead of laterad of the small terminal segment (Fig. 38), a very excep- 
tional situation. The location of this seta is normal in the first instar 
(Fig. 33), the unusual position found in the later instars being the result 
of its migration around the cephalic side of the distal segment. This process 
is unquestionably a recapitulation. 

The postembryology of the spinneret of noctuid larvae is a highly com- 
plicated and most interesting subject. Four distinct types of development 
of this structure have been observed and most probably a more extensive 
study will reveal the existence of a number of additional ones in the order. 
In Type I the spinnerets of both first and last instars are subequal in length 
and distinctly longer than in the intermediate stadia. The species of Phy- 
tometra examined present this condition. Type II is represented by 
Lycophotia margaritosa. The spinneret of the first instar of this species 
(Fig. 34) is much longer than the palpi and fairly slender, the condition 
most frequently found in the fully grown Jarvae thruout the family. In 
the second stadium it is very much shorter and reveals slight projections 
on both upper and lower distal margins (F.gs. 35, 36). The reduction in 
Jength proceeds a little further in the third instar and the distal projections 
become longer (Fig. 37). Moreover the lateral emarginations, which are 
very rudimentary in the first two stadia, are fairly deep in this one, so that 
the upper and lower lips, previously described, become evident. From this 
stadium to the last there is no appreciable change in relative length, but 
the projections gradually become elongated on both lips, forming a well 
developed fringe, and the proximal fold and its sclerite decrease consider- 
ably in relative width. The lower lip shows a tendency to become bilobed. 
The decrease in the relative size of the sensoria has already been discussed. 
Polia renigera exemplifies Type III. The spinneret of the first instar is 
somewhat shorter than the palpus (Figs. 29, 30). In the following stadia a 
gradual increase in its relative length occurs and the proximal fold becomes 
markedly elongated on the cephalic aspect. The condition in the fully 
grown larva is shown in Figures 31 and 32, where the spinning organ is 
somewhat longer than the palpi and the extension of the proximal fold 
reaches about half way to its distalend. The secondary chitinization of the 
spinneret and of the proximal fold, like that between the sensoria of the 
proximal sclerite, does not appear until the last instar. Type IV presents 
very little change in the relative length of the spinneret in different instars, 
as may be seen by comparing Figures 40, 41, 43, and 44, representing the 


72 ILLINOIS BIOLOGICAL MONOGRAPHS [314 


postembryology of the spinneret of Agrotis ypsilon, which typifies this type 
of development. The proximal sclerite descreases in relative width as in 
the other types. The fold in this species increases as it does in Polia reni- 
gera but to a much lesser extent. A secondary chitinization appears on the 
fold continuous with the primary sclerite but of a lighter color, again recall- 
ing the somewhat similar condition in renigera. The fringe develops much 
as in Lycophotia margaritosa, its first indication appearing as slight rounded 
projections on the upper lip of the second instar (Fig. 42). Unlike mar- 
garitosa, however, the lateral emarginations are well developed in this 
stadium and the distal projections appear only on the upper lip. In the 
following instars the lower lip becomes distinctly bilobed and a small 
fringe, which presents considerable individual variation, develops on the 
upper one from the projections which appear first in the second instar 
(Figs. 43-46). 

The essential basis for the recognition of these four types is the differ- 
ence in the relative length of the spinneret in different stadia. The other 
changes described will be considered later. In Type I the spinneret is 
longer in the first and last instars than in the others; in II it is long in the 
first stadium, becoming short in the course of development; the condition in 
III is exactly the opposite, the first instar having a short spinneret which 
develops into a long one; in IV it is short thruout all stadia. Each of these 
types of postembryonic development of this structure is correlated with a 
different distribution of the spinning habit with reference to the instars. 
The species falling under Type I, long in first and last stadia, spin threads 
in the first instar and a well developed cocoon in the last. In Type II, 
long to short, the first instar only spins silk, the cocoon-spinning habit 
having been entirely lost in correlation with subterranean pupation. Type 
IV, short thruout, has lost the spinning power in all stadia. 

These changes in the relative length of the spinneret during postem- 
bryonic development are obviously to be explained by the unequal function 
of this structure in different stadia rather than by recapitulation. Inas- 
much as the ancestral noctuid larva had a long, slender spinneret, as has 
been shown on the basis of morphological evidence, the expression of the 
recapitulative force would result in a relative shortening of this organ from 
first to last instars in those forms where the spinneret of the last stadium 
has been reduced. Whereas this condition is found in Type II, where the 
first instar spins silk and the last one does not, it fails to occur in IV, where 
the spinneret is short in all stadia, the spinning habit being absent thruout. 
Similarly species which have preserved the long ancestral spinneret in the 
last stadium would exhibit this condition in all instars, if recapitulation 
were the only factor operating, whereas marked inequality in the relative 
length of this organ in the different stadia is found in both Types I and III, 
where the spinneret is long in the last instar. This situation exemplifies 


315] NOCTUID LARVAE—RIPLEY 73 


what may prove to be a general zoological law, namely, When the expression 
of the recapitulative law conflicts with the development in successive instars 
of a series of adaptations to different functions, or to different degrees of the 
same function, the latter is dominant . 

In species where either all or none of the instars spin silk it might be 
argued that the recapitulative force would be allowed to express itself, since 
the factor of unequal function would be eliminated. Instances are rare in 
the Noctuidae where the larvae of all stadia spin silk in approximately pro- 
portionally equal amounts,as in the tent-caterpillar, Malacosoma americana. 
Sidemia devastatrix furnishes the only instance known in the Noctuidae 
where this habit appears to be equally developed thruout larval life, and 
the data in this case are not conclusive, since live larvae of only the first 
and last three stadia have been seen by the author. The first instar spins 
silk threads during the feeding period, the fourth and fifth form slight 
cocoons in which to molt and the last pupates within a cocoon. Since the 
long ancestral spinneret has been preserved in this species, the expression of 
recapitulation would not involve any postembryonic change and so far as 
known none occurs, the spinneret of al! stadia examined being long. Type 
IV presents the opposite condition where there is no silk-spinning in any 
stadium. In this type the recapitulative law is not followed with respect 
to the relative length of the spinneret, which remains approximately the 
same thruout larval development. 

An analysis of the possibilities with regard to the original use of the 
habit of spinning silk in the order and in the family reveals the fact that we 
cannot reasonably expect to encounter an expression of the recapitulative 
force in species where the factor of unequal function has been secondarily 
eliminated, as it has in Type IV. There are at least three ways in which 
this habit may have originated in the ancestral lepidopterous larva. It 
may have developed originally in the first instar, functioning as a means of 
dissemination by the wind, as it does in various existing species, or in some 
other capacity. Apparently better grounded is the hypothesis that the 
spinning of a cocoon by the fully grown larva represents the primitive 
condition, the other instars having in certain forms subsequently developed 
the habit of spinning threads. Perhaps most probable of all is the possi- 
bility that this habit was originally equally developed in all stadia, as it is 
now found in the case-bearers, tent caterpillars, borers which line their 
burrows and miners which line their mines with silk. The frequent occur- 
rence of this condition among larvae of the more generalized families lends 
weight to this view, altho the limitation of the spinning of silk to cocoon- 
spinning often met with thruout the order favors the conclusion that this 
situation is the ancestral one. 

However this may be, the very exceptional occurrence among noctuid 
larvae of the equal development of the silk-spinning habit in all stadia 


74 ILLINOIS BIOLOGICAL MONOGRAPHS [316 


strongly indicates that the spinneret functioned unequally in different 
instars in the primitive caterpillar of the family. The spinning of silk most 
probably occurred in the last instar or in both first and last, these two con- 
ditions being the only ones of general occurrence in forms which retain the 
primitive long spinneret in the fully grown larva. Thus the factor of 
unequal function in the postembryology of the spinneret of noctuid larvae 
is most probably an ancestral one. In Type IV this factor has become 
secondarily eliminated by the loss of the power to spin silk in both first and 
last instars. We cannot reasonably expect, therefore, that recapitulation 
would find expression in the postembryology of this type with respect to 
the relative length of the spinneret. 

As previously concluded in the treatment of the morphology of the 
spinneret the fringe is a specialization which has developed in correlation 
with the habit of subterranean pupation, apparently functioning as a brush 
for the lining of the earthen cell with a secretion of the silk-glands. The 
fact that it is well developed only in the last instar also supports this con- 
clusion. The four types of the development of the spinneret just discussed 
are based only on its relative length and do not apply to the fringe, which 
often appears in both Types II and IV where the reduced spinneret occurs 
in the last instar. The appearance of the fringe in postembryonic develop- 
ment apparently represents a recapitulation. Since it functions only in the 
last instar, however, the factor of unequal functions has operated in the 
same direction as the recapitulative force, so that this process is not the 
expression of recapitulation alone. It falls under the same group in our 
classification of postembryonic changes as the development of the adfrontal 
suture, recapitulative and adaptive to unequal function. 

The appearance of the lateral emarginations, which are present only in 
the reduced type of spinneret, have presumably developed in phylogeny as 
they do in postembryology. Since the upper and lower lips thus formed 
probably have to do with the function of the spinneret, which is performed 
only in the last instar, unequal function as well as recapitulation has oper- 
ated in the production of this postembryonic change. 

The appearance of the elongated proximal fold and of the secondary 
chitinization in the postembryonic development of Polia renigera (Figs. 29, 
32) also recapitulates the phylogeny. Since these structures serve as a 
support for the spinneret, which is functional only in the last instar, unequal 
function also plays its part in these changes, which are evidently to be 
regarded as recapitulative and adaptive to unequal function. 

The reduction in the relative width of the proximal sclerite is apparently 
of general occurrence within the family, this process always manifesting 
itself regardless of the trends of development along other lines. Until more 
definite knowledge is gained of the phylogeny of this sclerite no definite 
conclusion can be reached as to the significance of its reduction in relative 


317] NOCTUID LARVAE—RIPLEY 75 


width during larval life. The same may be said of the loss of the portion 
of the proximal sclerite which lies between the sensoria in the first instar of 
Lycophotia margaritosa. Since morphological evidence indicates that both 
the palpiger and the proximal sclerite of the spinneret in noctuid larvae 
represent the remnants of a more general chitinization, it seems probable 
that both of these changes are recapitulative. 

The taxonomic importance of the structure of the spinneret of the last 
instar has already been emphasized. It is obvious that the condition of 
this structure in the first instar also provides valuable phylogenetic infor- 
mation. In Lycophotia margaritosa and A grotis ypsilon, where the spinneret 
of the last instar is essentially of the same type, that of the newly hatched 
larva is strikingly different. These two species are both of the subfamily 
Agrotinae. The habit of spinning threads in the first stadium, nevertheless, 
is apparently a comparatively fundamental one, hence the extent of the 
development of the spinneret in this stage, which is correlated with this 
habit promises to serve as a fundamental guide to relationships. It is 
important, therefore, that all accounts of the development of caterpillars 
state the situation with regard to the form of this organ and with reference 
to the spinning of threads in all instars. On the basis of the limited amount 
of data available as to the occurrence of silk-spinning in the first instar of 
noctuid larvae no correlation with the mode of life is apparent. 


LARVAPODS 


In the morphological discussion of the larvapods it was noted that the 
ancestral condition, where the four median pairs are well-developed, has 
been retained in the majority of noctuid larvae, altho in certain sub- 
families the first one or two pairs tend to become reduced and are sometimes 
lacking. The incipient condition in the development of this specialization 
is exemplified by many Agrotinae, where the first two pairs are distinctly, 
altho not strikingly shorter than the others. In Catocala a more advanced 
condition is found, the first two pairs of larvapods being much smaller 
than the others. This process has proceeded still further in the specialized 
subfamily Hypeninae, where the first pair is without crochets or wanting 
altogether. The most specialized situation with respect to this process is 
exhibited by nearly all Phytometrinae, whose adults are undoubtedly 
among the most specialized noctuids, and by certain Catocalinae, such as 
Caenurgia, where the larvapods of only the fifth and sixth adbominal and 
of the anal segments remain. 

If the postembryonic development of the larvapods were to recapitulate 
their phylogeny, we should expect to find a relative decrease in the size of 
the first one or two pairs from the first to the last instars in forms where 
these larvapods are reduced in size in the fully grown larva. In species 
where the last instar lacks the first one or two pairs they would be found, 


76 ILLINOIS BIOLOGICAL MONOGRAPHS [318 


at least in a vestigial condition, in the newly hatched larvae, unless their 
loss took place sufficiently early in phylogeny to restrict their appearance 
in ontogeny to embryonic stages. Since these two pairs of larvapods are 
generally present in the Catocalinae, their absence being rather exceptional, 
and since Hampson has reported them present in one genus of the Phyto- 
metrinae, this latter possibility must be regarded as highly improbable. 

A study of the postembryology of these appendages reveals the fact 
that these hypothetical changes based on recapitulation alone are not found 
and that the reverse condition usually presents itself. Instead of becoming 
relatively smaller during the course of development, the first two pairs of 
larvapods typically increase in relative size from the first to the last stadia. 
Moreover, where they are wanting in the fully grown larva, no trace of them 
is found in the first instar. On the contrary, in certain genera of Agrotinae, 
Hadeninae, and Acronyctinae, the first pair is absolutely wanting in the 
first and second stadia, appearing in the third as a minute vestige and 
increasing in relative size thereafter. This condition is diametrically 
opposite to the one which would result from an expression of recapitula- 
tion. From these facts it may be stated conclusively that the appearance or 
the increase in the relative size of the first one or two pairs of larvapods in 
the postembryonic development of noctuid larvae are non-recapitulative 
changes, the effects of recapitulation having been completely obscured by 
other factors. 

The reduction or absence in lepidopterous larvae of the cephalic one, 
two or three pairs of larvapods is correlated with the peculiar biological 
characteristic of walking with a looping gait. Noctuid larvae with this 
gait have been referred to as semi-loopers as opposed to the loopers of the 
Geometridae, where this gait is even more pronounced, since but one pair 
of median larvapods persists in the larvae of this family. Caterpillars of 
this type, because of the longer steps which they are able to take, can travel 
more rapidly for the amount of energy expended than those which walk in 
the usual manner. It is a matter of simple mechanics that the looping gait 
is the more efficient from the point of view of rapid progress. Loopers 
appear to be generally more active than other caterpillars, altho certain 
arctiids whose aptitude for traveling at a high rate of speed is frequently 
displayed, furnish an exception to this rule. 

The evolution of this habit in the larvae of the Catocalinae, Phyto- 
metrinae, and Hypeninae is very probably to be accounted for by the 
advantage of rapid locomotion which is thereby undoubtedly gained. The 
looping gait enables these caterpillars to withdraw from undesirable situa- 
tions with the minimum loss of time and with the minimum amount of 
exposure to the attack of enemies. When dislodged from the trees or the 
plants upon which they feed, usually in more or less protected situations, or, 
in the case of most Catocalinae, from the twigs upon which they rest, in 


319] NOCTUID LARVAE—RIPLEY 77 


which situation they are protectively colored, those which can most rapidly 
regain a favorable environment must survive natural selection in the course 
of evolution. The many advantages gained by the power of rapid locomo- 
tion are so obvious that a detailed discussion of them would be superfluous. 
Larvae of the ground and subterranean strata enjoy protection in a large 
measure by virtue of their nocturnal and subterranean habits. The 
proximity of their food to the ground, moreover, requires but little climbing 
for them to reach it. In the older comparatively inactive larvae of such 
forms the reduction of the first two pairs of uropods is generally not pro- 
nounced. Caenurgia erechiea and certain phytometrids afford exceptions to 
this rule. The occupation of the field stratum by the former species is very 
unusual for larvae of the Catocalinae and is, therefore, to be regarded as a 
biological specialization. The loss of the larvapods very possibly took 
place in the ancestor of this species previous to its migration from the tree 
to the ground stratum. However, this may be, the looping habit in noctuid 
larvae appears to be generally correlated with a relatively active mode of 
life and with one which often renders rapid locomotion especially advan- 
tageous. It is never found among the cutworms or their biological allies, 
except in the earlier stadia, being usually confined to the first two. These 
instars are semiloopers in the family in all instances known to the author, 
regardless of the gait of the older larvae. In the earlier stadia the larvae 
are markedly more active than in the later ones. The small size and propor- 
tionately long setae of newly hatched caterpillars render them decidedly 
subject to conveyance by the wind, a matter of common observation. This 
fact necessitates that they be generally more active than the older instars. 
Moreover, the large number of individuals hatching simultaneously from a 
single egg-mass demands dissemination either by the wind or by locomo- 
tion, considerable activity being involved in either case. The threads 
frequently spun only by the first instar serve as veritable parachutes in 
some instances and as anchors by which they attach themselves to the food- 
plant in others. The former employment of the thread, however, has not 
been actually observed in the Noctuidae, so far as known, altho it has been 
reported in other families and most probably occurs in this one. The 
apparently universal presence of the looping gait in young noctuid larvae, 
which is characteristic of the last instars of only the more active larvae of 
the family, such as the catocalas, is not at all surprising when we consider 
the especial need for rapid locomotion during the first one or two stadia. 
The appearance or increase in the relative size of the first one or two 
pairs of larvapods during the postembryonic development of noctuid larvae 
is obviously the expression of the unequal function of these structures in 
different stadia. The extent of the reduction of these larvapods is propor- 
tional to the extent of the development of the looping gait, which is cor- 
related with the amount of advantage gained by greater or less rapidity in 


78 ILLINOIS BIOLOGICAL MONOGRAPHS [320 


locomotion, an advantage which is greater in the earlier instars than in the 
later, especially with noctuid larvae of the ground and subterranean strata. 
This factor of unequal function in different instars has completely obscured 
the effects of recapitulation, as in the parallel situation of the unequal 
function of the spinneret, which has been previously discussed. Thus 
additional support is given to the law stated to the effect than unequal 
function is dominant over recapitulation when these factors act in opposi- 
tion to one another. 

Henneguy states that the gaining of the first pair 78 larvapods occurs 
during postembryonic development in the European noctuids, Agrotis 
pronuba, (Agrotinae), Polia nebulosa (Hadeninae) and Trachea atriplicis 
(Acronyctinae). This condition has been found by the author in Agrotis 
ypsilon and in Feltia subgothica, altho the first pair of larvapods is fairly 
well developed in the first instars of Agrotis c-nigrum and badinodis. In 
Lycophotia margaritosa, of the same subfamily, they are present but ex- 
tremely vestigial, bearing only two or three crochets. A similar difference 
with respect to this point is also found in the genus Polia. The American 
renigera has the first pair of larvapods comparatively well developed in the 
first stadium, as does the rather closely related Ceramica picta, whereas 
they are reported absent in the European Polia nebulosa. In like manner 
they are not strikingly smaller than the second pair in the newly hatched 
larvae of Sidemia devastatrix, altho Henneguy states that they are absent 
in those of the closely related Trachea atriplicis. 

The difference in the development of the first pair of larvapods in 
closely related species indicates that this developmental character is not a 
fundamental one from the taxonomic point of view. The scattered occur- 
rence of their absence in the first two stadia thruout the subfamilies 
Agrotinae, Hadeninae, and Acronyctinae shows that this condition, like 
the length of the epicranial stem and like the number of molts, has origi- 
nated independently in different species. The tendency toward the reduc- 
tion of the first two pairs of larvapods is, however, general thruout the 
family. 

In the first instars of Catocala illia, amatrix, innubens, cara, and of 
Homoptera lunata the first two pairs are no more reduced than in the other 
subfamilies mentioned, altho the fully grown larvae of the Catocalinae are 
typically characterized by the very small size of the first two pairs of 
larvapods compared to the others. The tendency toward their marked 
reduction in this subfamily evidently applies to all stadia, rather than to 
the early ones alone, altho this process has advanced somewhat further in 
the young larvae than in the old ones, as it generally has throughout the 
family. The lack of striking difference between the relative size of the first 
two pairs of larvapods of the early instars and those of the later ones isa 
fundamental developmental character, which is evidently correlated with 
the active mode of life of the fully grown larvae of this subfamily. 


321] NOCTUID LARVAE—RIPLEY 79 


CROCHETS 


During the growth of noctuid larvae the number of crochets increases 
markedly on all of the larvapods. This process in Agrotis ypsilon may 
serve as a typical example. The formula for the first instar is -, 3, 5, 7, 8, 
the first pair of larvapods being absent, for the second it is -, 5, 7, 7, 8, for 
the third 3, 7, 9, 10, 14, for the fourth 9, 13, 13, 13, 16, for the fifth 12, 13, 
15, 16, 19, for the sixth 16, 18, 19, 19, 20, and for the fully grown larva it is 
16, 20, 20, 21, 25. Like the ocellarae and the sensoria the crochets are 
relatively much larger in the earlier than in the later stadia. Consequently 
there is sufficient space on the larvapods of the first instar to accommodate 
but relatively few crochets. A survey of the number found in the larvae 
of the more generalized families in the order, as well as in caterpillars gener- 
ally, offers absolutely no evidence favoring the view that this change is 
recapitulative. The increase in the number of crochets is apparently to be 
accounted for by the mechanics of growth. 

Generally throughout the order the larvapods whose distal ends have 
the greater diameter bear the larger number of crochets. This relation is 
also clearly revealed by the condition found in an individual larva whose 
different pairs of larvapods differ in size. Since, in such an individual, the 
crochets are of approximately the same size on both large and reduced 
larvapods, there is naturally a larger number of them on the former. Hence 
with the increase in the relative size of the first two pairs, previously 
discussed, the number of crochets increases proportionally. But this 
change in the relative size of the larvapods is due to unequal function, as 
already determined. Therefore, the increase in the number of the crochets 
on the first two pairs is unquestionably the expression of two factors, the 
mechanics of growth and unequal function. This change is, therefore, to 
be classified as mechanical-adaptive. 

The analogous process on the other pairs is, on the other hand, not 
influenced by the adaptive factor, since there is no appreciable change in 
the relative size of these larvapods during larval growth. Hence the 
mechanics of growth alone is responsible for this change. The fact that 
the increase in the number of the crochets of the first two pairs is con- 
siderably greater than that of the others is consistent with the compound 
nature of the former postembryonic change as opposed to the simple one 
of the latter. 


80 ILLINOIS BIOLOGICAL MONOGRAPHS [322 


SUMMARY 


The principal results yielded by this investigation of the postembry- 
ology of noctuid larvae may be summarized as follows: 

(1) The number of molts is characteristic of species, altho influenced 
to some extent by external factors. 

(2) The largest number of molts, the greatest amount of larval growth, 
and the highest fecundity are three mechanically correlated conditions. 

(3) These three conditions represent a specialization, the larger number 
of molts and higher fecundity having been derived from the smaller number, 
which is correlated with lower fecundity. 

(4) The conditions of larval growth, number of molts, and higher 
fecundity have arisen independently in different species. 

(5) An investigation of the postembryonic development of all external 
structures of noctuid larvae has revealed the existence of many previously 
undescribed changes. 

(6) Three factors have been identified as operating in the production of 
the changes observed, recapitulation, adaptation to unequal function in 
different stadia, and the mechanics of growth. 

(7) These factors may express themselves singly or in various combina- 
tions, in which case they may operate either in the same direction or in 
opposition to one another. 

(8) Recapitulation is essentially different from the other two factors in 
that it is the expression of a general law, which fails to manifest itself oniy 
when its effects are obscured by those of other factors. 

(9) When recapitulation and adaptation to unequal function con- 
flict, the latter is dominant. 

(10) When the factor of unequal function becomes secondarily elimi- 
nated, the recapitulative force remains unexpressed. 

(11) The postembryonic changes found have been classified according 
to the factor or combination of factors responsible for them. This classifi- 
cation is as follows: 

(I) Recapitulative—Changes in the relative length of the epicranial 
stem, in the extension mesad of the postgenae, and in the depth of the 
labral cleft; the migration ventrad of the occipital setae, of the head setae 
vi, v2,and probably f1; changes in the coloration of the head and body, in 
the sculpturing of the cuticle, in the location of the body-setae, except those 
of the first two pairs of larvapods, and in the form of the mandibles; the 
reduction of the primary chitinization and acquisition of secondary chitin- 


323] NOCTUID LARVAE—RIPLEY 81 


ization in the proximal sclerite of the spinneret; the migration mesad of the 
proximal seta of the labial palpus in Lycophotia; the secondary appearance 
of the tubercle of the seta rho in certain phytometrids. 

(II) Non-recapitulative—(a) Adaptive to unequal function in different 
stadia.— Changes in the form of the setae of the head and trunk and in the 
relative length of the spinneret; the acquisition of the first pair of larvapods; 
the increase in the relative size of the first two pairs of larvapods; changes 
in the position of the setae of these larvapods. (b) Due to the mechanics of 
growth.—The decrease in the relative size of the head, ocellarae, and sen- 
soria; the migration ventrad of the head-setae v2, v4, and v5; the increase 
in the number of the crochets of the larvapods of the fifth and sixth 
abdominal segments. 

(III) Compound, (a) recapitulative-adaptive-—The appearance of the 
adfrontal sutures; of the fringe, lips, and secondary chitinization of the 
spinneret; the elongation of the proximal fold of the spinneret. Compound, 
(b) adaptive-mechanical—tThe increase in the number of crochets of ae 
first two pairs of larvapods. atte 

(IV) Problematical—Changes in the form of the antennae,-'m’ “the 
relative size of the setae of the stipula, and in the form of the labial palpi; 
the reduction of the setae of the labial palpi and antennae; the: loss of the 
tubercles of the body-setae. 

(12) The great value of a comparative postembs} lite study of 
species as a source of phylogenetic information hasbeen demonstrated, 
chiefly by means of a detailed investigation of the: ‘development of the 
epicranial stem. 2 

(13) Different types of postembryonic ete Aa of various struc- 
tures, especially of the spinneret, epicranial stem, and larvapods, furnish 
developmental characters of considerable taxonomic importance. The 
condition of these structures should be given in detail in all descriptions of 
young caterpillars. The relative length of the spinneret of the first instar 
is especially important. The postembryonic development of the epicranial 
index offers an excellent means of determining relationships. 

(14) Various correlations between structural and biological postem- 
bryonic changes have been established, such as those between the relative 
length of the spinneret and the amount of silk spun in different stadia, 
between the development of the fringe of the spinneret and the habit of 
subterranean pupation, and between the acquisition or relative increase in 
size of the first pair of larvapods and the decrease in general activity. 

(15) The correlation between the subterranean mode of life, the resist- 
ance to submergence in water, and the short epicranial stem has been 
demonstrated. By virtue of this relation the postembryology of the 
epicranial stem has revealed the progressive nature and independent origin 
of the subterranean habit of noctuid larvae. 


82 ILLINOIS BIOLOGICAL MONOGRAPHS [324 


(16) The significance of the adfrontal suture has been determined upon 
the basis of postembryological evidence. This suture is a modification 
functioning as a means of ecdysis at the time of pupation. 

(17) Sensory hypodermis, such as that of the ocellarae and sensoria, 
does not grow as rapidly as the ordinary hypodermis. 


POSTSCRIPT 


Much of the data of this investigation is included in twelve statistical 
tables which were submitted with the manuscript. The intricacy of these 
tables is such that it has been impossible to reproduce them here. They 
were included in the original copy of the thesis which is deposited in the 
Library of the University of Illinois, where they can be consulted by those 
interested. 


6 


£088 ACKNOWLEDGMENTS 

Chief ‘among those to whom the author wishes to express his indebted- 
ness for their aid and encouragement during the progress of this investiga- 
tion is Dr. A. D.»MacGillivray. The value of his constant advice and 
suggestions, the fruition of a life-time study of the morphology of insects, 
could hardly be overzexpressed. His kindly interest has been a continued 
source of encouragement. The terms employed in his forthcoming “‘Exter- 
nal Insect-Anatomy”’ have been generously placed at the author’s disposal, 
so that much circumlocution and coining of new terms has been avoided. 

To Dr. S. A. Forbes the author wishes to express his sincere thanks for 
the use of the collection of the Illinois State Laboratory of Natural History. 
Since it has been necessary that practically all other material be collected 
and reared, the some thirty-five species of noctuid larvae in the collection 
were indispensible for the comparative morphological part of this work. 
Dr. C. P. Alexander and Mr. J. R. Malloch of the State Laboratory have 
extended numerous courtesies, which have aided very materially in the 
progress of these investigations and which are sincerely appreciated. 

For their general aid and encouragement the author is greatly indebted 
to Drs. V. E. Shelford, J. W. Folsom, R. D. Glasgow, and H. Yuasa. 
Certain of the experiments recorded above could not have been performed 
except by the use of the constant-temperature chambers in the Vivarium 
Building which were provided by funds from the Graduate School. 


325] NOCTUID LARVAE—RIPLEY 83 


BIBLIOGRAPHY 


BarneEs, W. and McDunnoveg, J. 
1917. Check list of the Lepidoptera of Boreal America. 392 pp. 
1918. Illustrations of the North America species of the genus Catocala. Mem. Am. 
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BERLESE, A. 
1909. Gli Insetti. Loro organizzazione, sviluppo, abitudini e rapporti coll’uomo. 
Societa Editrice Libraria. Vol. 1. 1004 pp. 
Branc, L. 
1891. La Tete du Bombyx mori a l’etat larvaire. Travaux du Laboratoire d’Etudes de 
la Soie; 180 pp. 
CarPENTER, G. H. and McDowE LL, MABEL. 
1912. The Mouth Parts of Some Beetle Larvae. Quart. Jour. Mic. Soc., 57:363-396. 
CHAPMAN, T. A. 
1894. Some Notes on the Micro-lepidoptera whose Larvae are External Feeders, and 
Chiefly on the Early Stages of Eriocephala calihella. Trans. Ent. Soc. London. 
335-350; pl. 6, 7. 
Crome, S. E. 
1915. A Key to the Cutworms Affecting Tobacco. Jour. Ec. Ent., 8:392-396; pl. 20. 
Dawrr, A. 
1910. Zur Kenntnis Gehanstragender Lepidopterenlarven. Zool. Jahrb., 12:513-608. 
Davis, J. J. and SATTErTHWAIT, A. F. 
1916. Life History Studies of Cirphis unipuncta, the True Army Worm. Jour. Agr. 
Resch. 6:799-812. 
Der Grysg, J. J. 
1915. Some Modifications of the Hypopharynx in Lepidopterous Larvae. Proc. Ent. 
Soc. Wash., 17:173-178; pl. 17-19. 
1916. The Hypermetamorphosis of the Lepidopterous Sapfeeders. Proc. Ent. Soc. 
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Dyar, H. G. 
1894. A Classification of Lepidopterous Larvae. Ann. N. Y. Acad. Sci., 8:194-232. 
1895. A Classification of Lepidoptera on Larval Characters, Amer. Nat., 29:1066-1072. 
1899. Descriptions of the Larvae of Fifty North American Noctuidae. Proc. Ent. Soc. 
’  Wash., 4:315-332. 
1901. A Century of Larval Descriptions. Entomologist’s Record, 13:37-41. 
1902. List of North American Lepidoptera and Key to the Literature of this Order of 
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Epwarps, H. 
1889. Bibliographical Catalogue of the Described Transformations of North American 
Lepidoptera. Bull. U. S. Nat. Mus., No. 35, 147 pp. 
FELT., E. P. 
1895. The Scorpion Flies. Rept. State Ent. N. Y., 10:463-479; pl. 3. 
Forses, S. A. 
1905. Rept. State Ent. Ill., 23:280 pp. 


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Forses, W. T. M. 
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1911. A Structural Study of the Caterpillars—II. The Sphingidae. Ann. Ent. Soc, 
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FRACKER, 5. B. 
1915. The Classification of Lepidopterous Larvae. Ill. Biol. Monog., 2:1-169; pl. 1-10. 
GacgE, J. H. 
1920. The Larvae of the Coccinellidae. Ill. Biol. Monog., 6:239-292; pl. 1-6. 
GooseEns, T. 
1898. Les Pattes des Chenilles. Ann. Soc. Ent. France, 7:385—404; pl. 7. 
Hampson, G. F. 
1903. Catalogue of the Lepidoptera Phalaenae, vol. 4-13. 
HE rnrIco, C. 
1916. On the Taxonomic Value of Some Larval Characters in the Lepidoptera. Proc. 
Ent. Soc. Wash., 18:154-164. 
Hewnecvy, L. F. 
1904. Les Insectes. Morphologie, reproduction, embryogenie. Paris. 804 pp. 
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1921. North American Caddis Fly Larvae. Bull. Lloyd Lib. Bot., Pharm., and Mater. 
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LyoneEt, P. 
1760. Traite Anatomique de la Chenille qui Rouge le Bois de Saule. La Haye. 616 pp. 
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MacGittiiveay, A. D. 
1923. External Insect Anatomy. A Guide to the Study of Insect Anatomy and an 
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McInpoo, N. E. 
1919. The Olfactory Sense of Lepidopterous Larvae. Ann. Ent. Soc. Amer., 12:65-84. 
PACKARD, A. S. 
1892. Notes on Some Points in the External Structure and Phylogeny of Lepidopterous 
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Payne, H. G. 
1918-19. (The life-histories in detail of various lepidopterous larvae). Proc. Ent. Soc. 
Nova Scotia; vols. 3, 4. 
SCHIERBECK, A. 
1917. On the Setal Pattern of Caterpillars and Pupae. Onderzoekingen Zool. Lab. 
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SHELFORD, V. E. 
1913. Animal Communities in North America as illustrated in the Chicago region. A 
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SmitH, J. B. 
1893. Catalogue of the Lepidopterous Superfamily Noctuidae found in Boreal North 
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SmiTH, J. B. and Dyar, H. G. 
1899. Contributions toward a Monograph of the Lepidopterous Family Noctuidae of 
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327] NOCTUID LARVAE—RIPLEY 85 


SUNDEVALL, C. J. ; 
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Akad. Stockholm. 


SwaAIn, J. M. 
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TicHomirorr, A. 
1879. Uber die Entwickelungsgeschicts des Seidenwurms. Zool. Anz., 2:64-69. 
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1913. Contributions towards the Comparative Morphology of the Trophi of the Lepi- 
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Tsou, Y. H. 
1914. The Body Setae of Lepidopterous Larvae. Trans. Amer. Mic. Soc. 33:233-260; 
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Yuasa, H. 
1920. The Anatomy of the Head and Mouth-parts of Orthoptera and Euplexoptera. 
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pls. 1-14. 


HH 


. us as ae i na 


a ie 
i bana 


329] 


NOCTUID LARVAE—RIPLEY 


PLATE I 


87 


88 


oN AN ew Ne 


‘oO 


ILLINOIS BIOLOGICAL MONOGRAPHS 


[330 


EXPLANATION OF PLATE I 
POSTEMBRYOLOGY OF THE EPICRANIAL STEM 


GRAPHIC REPRESENTATION OF THE EPICRANIAL INDEX. 
EACH SPECIES REPRESENTED BY A CURVE 


. Felita gladiaria (Noctuidae). 

. Conistra sp. (Noctuidae). 

. Catocala amatrix (Noctuidae). 

. Catocala ?vidua (Noctuidae). 

. Vitula edmansii (Pyralidae). 

. Agrotis ypsilon (Noctuidae). 

. Catocala cara (Noctuidae). 

. Feltia subgothica (Noctuidae). 

. Ceramica picta (Noctuidae). 

. Agrotis c-nigrum (Noctuidae). 

. Sidemia devastairix (Noctuidae). 

. Polia meditata (Noctuidae). 

. Polia renigera (Noctuidae). 

. Lycophotia margaritosa (Noctuidae). 
. Phytometra biloba (Noctuidae). 

. Phytometra brassicae (Noctuidae). 
. Catocala sp. (Noctuidae). 


18. 
1) 
20. 
21. 
22: 
23. 
24. 
25. 
26. 
21. 
28. 
29. 
30. 
31. 
32. 
33. 


Dipierygia scabriuscula (Noctuidae). 
Prodenia ornithogalli (Noctuidae). 
Cirphis unipuncta (Noctuidae). 
Agrotis clandestina (Noctuidae). 
Caenurgia erechtea (Noctuidae). 
Homoptera lunata (Noctuidae). 
Nephelodes emmedonia (Noctuidae). 
Thyridopteryx ephemeraeformis (Psychidae). 
Cirphis ?pseudargyria (Noctuidae). 
Hemerocampa leucostigma (Liparidae). 
Papaipema nebris (Noctuidae). 
Epizeuxis lubricolis (Noctuidae). 
Laphrygma frugiferda (Noctuidae). 
Homoptera lunifera (Noctuidae). 
Cirphis phragmitidicola (Noctuidae). 
Heterocampa bilineata (Notodontidae). 


ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME VIII 


1 2 3 4 B 
atee douasvanad Gazeveezeis HEH fel iestesaceetl i 
ee ga 
rath C anneu8 EEE 
+H PEELE LH EEE BEEEEEEE 
2 Hy Audie 
i rE EEE aii 
He a eatiees He 
FHEEEH PEEP 
Hi 
4 5 6 


3 
STADIUM 


RIPLEY NOCTUID LARVAE PLATE I 


331] 


NOCTUID LARVAE—RIPLEY 


PEATE Il 


89 


90 ILLINOIS BIOLOGICAL MONOGRAPHS 


EXPLANATION OF PLATE II 


EPICRANIAL STEM AND TENTORIUM 


[332 


1. Cirphis unipunctla, last instar, transverse section thru front and adfrontals, soft parts 


removed by potash. 


2. Cuirphis unipuncta, last instar, cephalic aspect of head. 


2a. Cirph’s unipuncta, last instar, dorsal portion of vertex and cervacoria. 


Zeuzera pyrina (Cossidae), last instar, postgenal region, ental aspect. 
A pyralid, last instar, postgenal region, ectal aspect. 


Thyridoptervx ephemeraeformis (Psychidae), young larva, postgenal region, ectal aspect. 


3 
4. 
5. Cacoecia sp. (Tortricidae), last instar, postgenal region, ectal aspect. 
6 
7 


Thyr‘dopteryx ephemeraeformis, last instar, postgenal region, ectal aspect. 


a antenna 

adf adfrontal sclerite 

adt adfrontal suture 

an  amntacoria 

cc cervacoria 

cca attachment of cervacoria 
ccc chitinized cervacoria 
cls clypeo-labral suture 
cs  clypeal suture 

ct corpotentorium 

ea epicranial arm 

epm epicranial parademe 
es epicranial stem 

ess epicranial suture 

f front 

fcs fronto-clypeal suture 
fs frontal sensorium 

t labrum 

ii = labium 

mi-2 mandibular setae 


voI-9 


mandible 
metatentorium 
maxilla 

occipital setae 
ocellarae 
occipital foramen 
postgena 
postgenal parademe 
preclypeus 
paracoila 
parademe 
precoila 


secondary postgenal suture 


pretentorium 
postcoila 
secondary of suture 
sensoria vertex 
vertex 

setae of vertex. 


ILLINOIS BIOLOGICAL MONOGRAPHS 


VOLUME VIII 


RIPLEY NOCTUID LARVAE 


PEALE 


II 


333| 


NOCTUID LARVAE—RIPLEY 


PLATE Iil 


91 


ILLINOIS BIOLOGICAL MONOGRAPHS [334 


EXPLANATION OF PLATE III 


CAUDAL ASPECT OF HEAD, TENTORIUM, POSTGENA 


. Epargyreous tityrus (Hesperiidae), last instar, postgenal region, ectal aspect. 
. Cirphis unipuncta, last instar, caudal aspect of head. 

. Polia renigera, last instar, postgenal region, ectal aspect. 

. Nephelodes emm:donia, last instar, postgenal region, ectal aspect. 

. Feltia subgothica, last instar, postgenal region, ectal aspect. 

. Cirphis unipuncta, last instar, cephalic aspect of head, ental surface. 

. Cirphis unipuncta, last instar, caudal aspect of head, ental surface. 


antenna pap 
antennaria pas 
cervacoria pl 
attachment of cervacoria pm 
chitinized cervacoria pox 
corpotentorium pr 
epicranial parademe pse 
epipharynx pt 
metatentorium pil 
ocl-6 ocellarae se 
occipital foramen td 
postgena tm 


postgenal parademe 
postgenal sensorium 
paracoila 

parademe 
postpharynx 
precoila 

secondary postgenal suture 
pretentorium 
postcoila 

secondary suture 
tendon 

torma 


vl—13 setae of vertex 


ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME VIII 


RIPLEY NOCTUID LARVAE PLATE III 


Kit, 


. 


re 


> 
— 
S 

# 
’y 
7 


ae | 


4 


335] 


NOCTUID LARVAE—RIPLEY 


PLATE IV 


93 


94 ; ILLINOIS BIOLOGICAL MONOGRAPHS [336 


EXPLANATION OF PLATE IV 


CEPHALIC ASPECT OF HEAD 


15. Feltia subgothica, last instar, cephalic aspect of head. 
16. Polia renigera, last instar, cephalic aspect of head. 
16a. Polia renigera, first instar, cephalic aspect of head. 
17. Chloridea armigera, last instar, cephalic of head. 


a antenna 

al—2 adfrontal setae 

adf adfrontal sclerite 
ads adfrontal sensorium 
adt adfrontal suture 

an antacoria 

ar antennaria 

cl-2 clypeal setae 

c¢ ~—scervacoria 

cls __clypeo-labral suture 
cs __ clypeal suture 

ea = epicranial arm 

es __ epicranial stem 

f front 

fl __ frontal setae 


fcs fronto-clypeal suture 
fs frontal sensorium 


1 labrum 

11-6 labral setae 
m1—2 mandibular setae 
md mandible 

ol—3 occipital setae 
oc1-6 ocellarae 

be  preclypeus 

po  postclypeus 

pr precoila 

sv1—3 vertical sensoria 
v vertex 

v1-13 vertical setae 


ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME VIII 


RIPLEY NOCTUID LARVAE PLATE IV 


a 


337] 


NOCTUID LARVAE—RIPLEY 


PLATE V 


95 


96 ILLINOIS BIOLOGICAL MONOGRAPHS [338 


EXPLANATION OF PLATE V 


HEAD ANP MOUTH-PARTS 


18. Ceramice picta, last instar, cephalic aspect of head. 

19. Cirphis unipuncta, last instar, cephalic aspect of right antenna. 

20. Cirph.s unipuncta, last instar, distal end of antenna. 

21. Cirphis unipuncta, last instar, diagram of distal end of antenna. 

22. Cirphis unipuncta, last instar, lateral aspect of right mandible. 

23. Cirph?s unipuncta, last instar, mesal aspect of right antenna. 

24. Cirphis unipuncta, last instar, caudal aspect of labium and mazxillae. 
24a. Cirphis unipuncta, last instar, distal end of maxilla, caudal aspect. 

25. Cirphis unipuncta, last instar, hypopharynx and cephalic aspect of labium and mazxillae. 
26. Cirphis unipuncta, last instar, distal portion of labium, caudal aspect. 
27. Cirphis unipuncta, last instar, distal portion of labium, cephalic aspect. 


a antenna 

al-2 adfrontal setae 

adf adfrontal sclerite 
ads adfrontal sensorium 
adt adfrontal suture 

al _alacardo 

an  antacoria 

ar  antennaria 

cl-2 clypeal setae 

cc —_—cervacoria 

cls _clypeo-labral suture 
cs clypeal suture 

dg  distagalea 

ea epicranial arm 

es epicranial stem 

et extensotendon 

f front 

fl _ frontal setal 

fcs fronto-clypeal suture 
fs frontal sensorium 
hx hypopharynx 

hxs hypopharyngeal setae 
l labrum 

11-6 labral setae 

la _lacinia 

lp labial palpus 

m1-2 mandibular setae 


md mandible 

mdc mandacoria 

mp maxillary palpus 
ol-3 occipital setae 
pe _ preclypeus 

pl paracoila 

po postclypeus 


bp palpiger 

pr precoila 

pic  postartis 

py preartis 

rt —_ recto-tendon 
s stipes 


sa subcardo 

se secondary suture 

si spinneret 

sif fringe of spinneret 

sio proximal fold of spinneret 
sis proximal sclerite of spinneret 
sm submentum 

sp stipulae 

spr sensoria of palpiger 

sps  stipular setae 

sr sensorium 

svl-3 vertical sensoria 

v vertex 

v1-13 vertical setae 


ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME VIII 


ANAT 


sif hxs- 


RIPLEY NOCTUID LARVAE PLATE V 


339} 


NOCTUID LARVAE—RIPLEY 


PLATE VI 


97 


98 


ILLINOIS BIOLOGICAL MONOGRAPHS 


EXPLANATION OF PLATE VI 


LABIUM AND SPINNERET 


. Ceramica picta, last instar, distal portion of labium, caudal aspect. 

. Polia renigera, first instar, lateral aspect of spinneret. 

. Polia renigera, first instar, labial palpus. 

. Polia renigero, last instar, distal end of labium, caudal aspect. 

. Polia renigera, last instar, lateral aspect of spinneret. 

. Lycophotia margaritosa, first instar, distal end of labium, caudal aspect. 
. Lycophotia margaritosa, first instar, lateral aspect of spinneret. 

. Lycophotia margaritosa, second instar, lateral aspect of spinneret. 

. Lycophotia margaritosa, second instar, caudal aspect of spinneret. 


37. Lycophotia margaritosa, third instar, cephalic aspect of spinneret. 

38. Lycophotia margaritosa, last instar, distal portion of labium, caudal aspect. 
hsx hypopharyngeal setae stu upper lip of spinneret 

lp labial palpus siw lower lip of spinneret 

sd silk duct sp stipulae 

st spinneret spr sensoria of palpiger 

sif fringe of spinneret sps_stipular setae 

sio proximal fold of spinneret sf sensorium 

siy rudimentary fringe of spinneret ss secondary sclerite 

sis proximal sclerite of spinneret 


[340 


ILLINOIS BIOLOGICAL MONOGRAPHS 


VOLUME VIII 


RIPLEY NOCTUID LARVAE 


PLATE VI 


341] 


NOCTUID LARVAE—RIPLEY 


PLATE VII 


99 


100 


ILLINOIS BIOLOGICAL MONOGRAPHS [342 


EXPLANATION OF PLATE VII 


SPINNERET 


. Lycophotia margaritosa, last instar, cephalic aspect of spinneret. 

. Agrotis ypsilon, first instar, distal portion of labium, caudal aspect. 
. Agrotis ypsilon, second instar, caudal aspect of spinneret. 

. Agrotis ypsilon, second instar, cephalic aspect of spinneret. 

. Agrotis ypsilon, third instar, distal portion of labium, caudal aspect. 
. Agrotis ypsilon, last instar, distal portion of labium, caudal aspect. 

. Agrotis ypsilon, last instar, lateral aspect of spinneret. 

. Agrotis ypsilon, last instar, cephalic aspect of spinneret. 


hypopharyngeal setae sis proximal sclerite of spinneret 
labial palpus siu upper lip of spinneret 
palpiger siw lower lip of spinneret 
spinneret sp stipulae 

fringe of spinneret spr sensoria of palpiger 
proximal fold of spinneret sps stipular setae 


rudimentary fringe of spinneret sf sensorium 


ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME VIII 


RIPLEY NOCTUID LARVAE PLATE VIL 


143] 


NOCTUID LARVAE—RIPLEY 


PLATE VIII 


101 


102 


ILLINOIS BIOLOGICAL MONOGRAPHS [344 


a 


2 
2, @JEXPLANATION OF PLATE VIII 
*) 


THORACIC AND ABDOMINAL SETAE, LEGS 


47. Cirphis unipuncta, last instar, setal maps of thoracic and first abdominal segments. 
48. Cirphis unipuncta, last instar, setal maps of second, third, fourth, and fifth abdominal 


segments. 


49. Cirphis unipuncta, last instar, setal maps of seventh, eighth, ninth, and tenth abdominal 


segments. 


50. Cirphis unipuncta, last instar, a median larvapod, lateral aspect. 

51. Cirphis unipuncta, last instar, a median larvapod, mesal aspect. 

52. Cirphis unipuncta, last instar, anal larvapod, mesal aspect. 

53. Scolecocampa liburna, last instar, and larvapod, lateral aspect. 

54. Cirphis unipuncta, last instar, prothoracic leg, cephalic aspect. 

55. Cirphis unipuncta, last instar, prothoracic leg, caudal aspect. 

56. Cirphis unipuncta, last instar, claw of prothoracic leg. 

57. Cirphis unipuncta, last instar, distal portion of a median larvapod, distal aspect. 

58. Cirphis unipuncta, last instar, distal portion of a median larvapod, mesal aspect. 

59. Cirphis unipuncta, last instar, mesal aspect of crochets. 

60. Diagram representing the phylogeny of the short epicranial stem as derived from a 
study confined to the last instar. Erroneous interpretation. 

61. Diagram representing the phylogeny of the short epicranial stem as derived from postem- 
bryological study. Correct interpretation. 


co _ crochet 


cw claw 

cz coxa 

fe femur 
lop larvapod 


Be Jo 


ma 
Yd 
t 
ts 


muscle attachment 
sensorium 
tibia 

tarsus 


ILLINOIS BIOLOGICAL MONOGRAPHS 


VOLUME VIII 


persistent 
ane. Fi 


5 4 3 2 
shortest stem 
most specialized-—> 


long stem 


ancestral condition- 


60 


=m 


RIPLEY NOCTUID, LARVAE, »», 


5) 
PTE 9 923 95? 
2332330903 ) 25 2 

Oe Fes sien a sia 4 sisi es OeD aD: 

ids Yoke >a3 > 9D. 

9. 2, 8. > 2 J 


Snortesi stem 


Most specialized---- 


jong stem 
- ancestral condition--- 


61 


D9 0 
Be Le, 


2, 2, PLATE VIII 


ce 
: ¢. 
re) et 
etuer: 
mtd (ef, aor 


ni 


